def construct(self):
t1 = TextMobject(
"Let's look at our \\texttt{power(x,n)} function from Part 1 again"
)
t1.to_edge(UP)
power1_code = CodeBlock(
'Java', r"""
public static int power(int x, int n) {
if (n == 0) {
return 1;
}
int t = power(x, n - 1);
return x * t;
}
""")
power1_code.next_to(t1, DOWN, buff=MED_LARGE_BUFF)
self.play(
FadeIn(t1),
FadeIn(power1_code),
)
self.wait()
t2 = TextMobject("How many times does it call itself?")
t2.next_to(power1_code, DOWN, buff=MED_LARGE_BUFF)
self.play(Write(t2))
self.wait(duration=2)
t3 = TextMobject(
"It call's itself $n$ times. Recall our original equation:")
t3.move_to(t2)
f1 = TexMobject('x^n=', 'x \\times x \\times ... \\times x',
'= x \\times x^{n-1}')
f1.next_to(t3, DOWN)
b1 = BraceLabel(f1[1],
'$n$ times',
brace_direction=DOWN,
label_constructor=TextMobject)
f1 = VGroup(f1, b1)
hr = SurroundingRectangle(power1_code.get_code().get_lines(5)[-5:-2])
self.play(ReplacementTransform(t2, t3), FadeInFromDown(f1), FadeIn(hr))
self.wait(duration=4)
t4 = TextMobject('Can we do better?')
self.play(*[FadeOut(o) for o in self.mobjects], FadeIn(t4))
self.wait()
self.play(FadeOut(t4))
def get_fib_code(self, scale):
return CodeBlock(
'Java',
r"""
public static int fib(int n) {
if (n == 0) {
return 0;
}
if (n == 1) {
return 1;
}
int fn1 = fib(n - 1);
int fn2 = fib(n - 2);
return fn1 + fn2;
}
""",
code_scale=scale,
)
def construct(self):
# Look at power1() and highlight parts of it. Anatomy of a recursive function.
# Always has two parts: base case and recursive step.
code_scale = 0.75
power_code = CodeBlock(
'Java',
r"""
public static int power(int x, int n) {
if (n == 0) {
return 1;
}
int t = power(x, n - 1);
return x * t;
}
""",
code_scale=code_scale,
)
power_code.to_edge(UP)
self.add(power_code)
self.wait()
title = TextMobject('Anatomy of a Recursive Function').to_edge(UP)
power_code.generate_target()
power_code.target.next_to(title, DOWN, buff=MED_LARGE_BUFF)
self.play(
FadeInFrom(title, UP),
MoveToTarget(power_code),
)
self.wait()
pc_groups = [
VGroup(power_code.get_code().get_lines(p))
for p in [(1, 2), (2, 5), (5, 7), (7, 8)]
]
pc_t = [g.generate_target() for g in pc_groups]
# Base Case
# - All of these have a base case that ends the recursion and returns.
# - Computed directly from the inputs.
# - Base cases are often some variant of emptiness. Power1() is a good example, with n == 0.
# What if you returned x for n == 1?
base_shifts = [UP * 6, DOWN, DOWN * 6, DOWN * 6]
power_code.save_state()
for t, s in zip(pc_t, base_shifts):
t.shift(s)
t1 = TextMobject('Base Case').next_to(title, DOWN, buff=0.75)
self.play(
*[MoveToTarget(o) for o in pc_groups],
FadeIn(t1),
)
self.wait()
points_dwell_time = 2.5
t2 = TextMobject(
"- stops the recursion and returns\\\\",
"- value is computed directly from the inputs, or constant\\\\",
"- often it's some form of ``emptiness'' or ``singleness''\\\\",
alignment="").next_to(title, DOWN, buff=LARGE_BUFF * 3.5)
base_highlights = [
SurroundingRectangle(pc_groups[1][0][1][0:6]),
SurroundingRectangle(pc_groups[1][0][1][6:7]),
SurroundingRectangle(pc_groups[1][0][0][3:7]),
]
for t, h, ph in zip(t2, base_highlights, [None] + base_highlights):
opt_anim = [FadeOut(ph)] if ph else []
self.play(
*opt_anim,
FadeInFromDown(t),
FadeIn(h),
)
self.wait(duration=points_dwell_time)
self.play(FadeOut(base_highlights[-1]))
self.wait()
self.play(
FadeOut(t1),
FadeOut(t2),
power_code.restore,
)
self.wait()
# Recursive Step
# The recursive step is some variant of decompose/reduce, call, recombine/compute.
# - Recursive case: compute the result with the help of one or more recursive calls to the same function.
# In this case, the data is reduced in some way in either size, complexity, or both.
# - In this case, reducing n by 1 each time.
pc_t = [g.generate_target() for g in pc_groups]
recurse_shifts = [UP * 6, UP * 6, UP * 0.45, DOWN * 6]
power_code.save_state()
for t, s in zip(pc_t, recurse_shifts):
if s is not None:
t.shift(s)
t1 = TextMobject('Recursive Step').next_to(title, DOWN, buff=0.75)
self.play(
*[MoveToTarget(o) for o in pc_groups],
FadeIn(t1),
)
self.wait()
t2 = TextMobject(
"- reduce: make the problem smaller, or break it into parts\\\\",
"- call: one or more recursive calls\\\\",
"- recombine: compute the result from the pieces\\\\",
alignment="").next_to(title, DOWN, buff=LARGE_BUFF * 3.5)
# 012345678901234567
# intt=power(x,n-1);
# returnx*t;
recurse_highlights = [
SurroundingRectangle(pc_groups[2][0][0][13:16]),
SurroundingRectangle(pc_groups[2][0][0][5:17]),
SurroundingRectangle(pc_groups[2][0][1][6:9]),
]
for t, h, ph in zip(t2, recurse_highlights,
[None, *recurse_highlights]):
opt_anim = [FadeOut(ph)] if ph else []
self.play(
*opt_anim,
FadeInFromDown(t),
FadeIn(h),
)
self.wait(duration=points_dwell_time)
self.play(FadeOut(recurse_highlights[-1]))
self.wait()
self.play(
FadeOut(t1),
FadeOut(t2),
power_code.restore,
)
self.wait(0.5)
power_code.generate_target()
power_code.target.to_edge(RIGHT)
bcb = BraceLabel(power_code.target.get_code().get_lines((2, 5)),
'\\textit{Base Case}',
brace_direction=LEFT,
label_constructor=TextMobject,
buff=LARGE_BUFF)
rsb = BraceLabel(power_code.target.get_code().get_lines((5, 7)),
'\\textit{Recursive Step}',
brace_direction=LEFT,
label_constructor=TextMobject,
buff=LARGE_BUFF)
self.play(MoveToTarget(power_code), )
self.play(
ShowCreation(bcb),
ShowCreation(rsb),
)
self.wait(0.5)
t1 = TextMobject('Base Case', ':', ' stops the recursion')
t2 = TextMobject('Recursive Step', ':', ' reduce - call - recombine')
t2.next_to(t1.get_part_by_tex(':'),
DOWN,
submobject_to_align=t2.get_part_by_tex(':'),
buff=MED_LARGE_BUFF)
g = VGroup(t1, t2).shift(DOWN * 1.5)
self.play(FadeIn(g))
self.wait(duration=points_dwell_time)
t3 = TextMobject(
"In Part 2 we'll look at making this function more efficient!"
).scale(0.75)
t3.to_edge(DOWN).set_color(BLUE)
self.play(Write(t3))
# self.play(*[FadeOut(o) for o in self.mobjects])
self.wait(duration=3)
end_scale_group = VGroup(*self.mobjects)
end_fade_group = VGroup(t3, title)
self.animate_yt_end_screen(end_scale_group,
end_fade_group,
show_elements=False)
def construct(self):
code_scale = 0.75
ss_code = CodeBlock(
'Java',
r"""
public static double StrangeSqrt(double a) {
if (a < 0) {
double b = StrangeSqrt(a * -1);
return b;
}
return Math.sqrt(a);
}
""",
code_scale=code_scale,
)
t1 = TextMobject(
'Consider this somewhat strange square root function:')
t1.next_to(ss_code, UP, buff=LARGE_BUFF)
self.play(
FadeIn(t1),
ShowCreation(ss_code),
)
self.wait(duration=2.5)
t2 = TextMobject(
'It has a recursive call, meaning \\textit{it calls itself.}')
t2.next_to(ss_code, DOWN, buff=LARGE_BUFF)
# 012345 6 7 8901234567890 1 2345
# double b = StrangeSqrt(a * -1);
rl = ss_code.get_code().get_lines(3)
rc_highlight = SurroundingRectangle(rl[8:-1])
self.play(
FadeIn(t2),
FadeIn(rc_highlight),
)
self.wait(duration=3)
self.play(
FadeOut(t2),
FadeOut(rc_highlight),
)
# Run with a positive input
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
double n = StrangeSqrt(4);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
frame_width = 3.5
main_frame = StackFrame(main_code,
'main()',
9, ['n'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
t3 = TextMobject("Let's see what it does with a positive input...")\
.next_to(ss_code, DOWN, buff=LARGE_BUFF)
self.play(
FadeOut(t1),
MaintainPositionRelativeTo(t1, ss_code),
ss_code.to_edge,
UP,
FadeIn(t3),
MaintainPositionRelativeTo(t3, ss_code),
)
self.wait()
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
ss_frame = StackFrame(ss_code,
'StrangeSqrt(4)',
1, ['a', 'b'],
width=frame_width)
ss_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(ss_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(ss_frame, UP),
FadeOut(t3),
)
ss_code.post_control_transfer(xi, self)
self.wait()
self.play(
ss_code.highlight_lines,
2,
ss_frame.set_line,
2,
ss_frame.update_slot,
'a',
4,
)
self.wait()
self.play(
ss_code.highlight_lines,
6,
ss_frame.set_line,
6,
)
self.wait()
xi = ss_code.pre_return(main_code, 9)
self.play(
*ss_code.get_control_transfer_clockwise(xi),
Uncreate(ss_frame),
)
main_code.post_control_transfer(xi, self)
self.wait()
t1 = TextMobject('That seems pretty normal...').next_to(
ss_code, DOWN, buff=LARGE_BUFF)
self.play(
main_code.highlight_lines,
10,
main_frame.set_line,
10,
main_frame.update_slot,
'n',
2,
FadeIn(t1),
)
self.wait(duration=2)
t2 = TextMobject("Let's try it with a negative input...")\
.next_to(ss_code, DOWN, buff=LARGE_BUFF)
self.play(
FadeOutAndShiftDown(main_code),
FadeOutAndShiftDown(main_frame),
FadeOut(t1),
FadeIn(t2),
)
# Run with a negative input and see the recursion
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
double n = StrangeSqrt(-4);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
main_frame = StackFrame(main_code,
'main()',
9, ['n'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
ss_frame = StackFrame(ss_code,
'StrangeSqrt(-4)',
1, ['a', 'b'],
width=frame_width)
ss_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(ss_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(ss_frame, UP),
FadeOut(t2),
)
ss_code.post_control_transfer(xi, self)
self.wait()
self.play(
ss_code.highlight_lines,
2,
ss_frame.set_line,
2,
ss_frame.update_slot,
'a',
-4,
)
self.wait()
self.play(
ss_code.highlight_lines,
3,
ss_frame.set_line,
3,
)
self.wait()
self.play(Indicate(rl[8:-1]), )
ss2_frame = StackFrame(ss_code,
'StrangeSqrt(4)',
1, ['a', 'b'],
width=frame_width)
ss2_frame.next_to(ss_frame, UP, buff=SMALL_BUFF)
r1_call_site_rect = ss_code.get_current_highlight().copy().set_color(
WHITE)
self.play(
FadeInFrom(ss2_frame, UP),
ss_code.highlight_lines,
1,
FadeIn(r1_call_site_rect),
)
self.wait()
stack = VGroup(main_frame, ss_frame, ss2_frame)
t1 = TextMobject('Same function, but with\\\\a new frame on the stack')\
.next_to(stack, LEFT, buff=LARGE_BUFF).shift(UP * 0.5)
a = Arrow(t1.get_right(), ss2_frame.get_left(), stroke_width=3)
self.play(
FadeIn(t1),
GrowArrow(a),
)
self.wait(duration=2)
# Now we have a positive input again
self.play(
ss_code.highlight_lines,
2,
ss2_frame.set_line,
2,
ss2_frame.update_slot,
'a',
4,
)
self.wait()
self.play(
ss_code.highlight_lines,
6,
ss2_frame.set_line,
6,
FadeOut(t1),
FadeOut(a),
)
self.wait()
t1 = TextMobject('The stack tells us where to return,\\\\and with which values')\
.next_to(stack, LEFT, buff=LARGE_BUFF).shift(UP * 0.5)
a = Arrow(t1.get_right(), ss_frame.get_left(), stroke_width=3)
self.play(
FadeIn(t1),
GrowArrow(a),
)
self.wait(duration=2)
# Return back to line 3...
self.play(
FadeOut(r1_call_site_rect),
Uncreate(ss2_frame),
ss_code.highlight_lines,
3,
ss_frame.set_line,
3,
)
self.wait()
self.play(
ss_code.highlight_lines,
4,
ss_frame.set_line,
4,
ss_frame.update_slot,
'b',
2,
FadeOut(t1),
FadeOut(a),
)
self.wait()
xi = ss_code.pre_return(main_code, 9)
self.play(
*ss_code.get_control_transfer_clockwise(xi),
Uncreate(ss_frame),
)
main_code.post_control_transfer(xi, self)
self.wait()
self.play(
main_code.highlight_lines,
10,
main_frame.set_line,
10,
main_frame.update_slot,
'n',
2,
)
self.wait()
t1 = TextMobject(
'Thinking about the call stack can help you keep track of\\\\'
'what a recursive function is doing at any given moment.').next_to(
ss_code, DOWN, buff=LARGE_BUFF)
self.play(
FadeOutAndShiftDown(main_code),
FadeOutAndShiftDown(main_frame),
FadeIn(t1),
)
self.wait(duration=3)
t2 = TextMobject('Try writing down part of the stack as you go.')\
.next_to(t2, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromDown(t2))
self.wait(duration=2)
self.play(
FadeOut(t1),
FadeOut(t2),
)
self.wait()
def construct(self):
t1 = TextMobject("Let's compute $x^n$").shift(UP)
self.play(FadeIn(t1))
self.wait()
t2 = TextMobject("i.e., $2^4=16$, or $4^3=64$, etc.")
t2.next_to(t1, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromDown(t2))
self.wait(duration=2)
t3 = TextMobject('Recall that')
f1 = TexMobject('x^n=', 'x', '\\times', 'x \\times ... \\times x',
'x^{n-1}')
f2 = TexMobject('x^n=', 'x', '\\times', 'x^{n-1}')
f2.next_to(t3, RIGHT)
dg = VGroup(t3, f2).center().shift(
UP) # Place t3 so the final result is centered
f1.next_to(t3, RIGHT)
b1 = BraceLabel(f1[1:-1],
'$n$ times',
brace_direction=UP,
label_constructor=TextMobject)
g = VGroup(t3, f1[:-1], b1) # For display
self.play(
FadeOut(t1),
FadeOut(t2),
FadeInFromDown(g),
)
self.wait(duration=3)
b2 = BraceLabel(f1[3],
'$n-1$ times',
brace_direction=UP,
label_constructor=TextMobject)
self.play(ReplacementTransform(b1, b2), )
self.wait(duration=2)
self.play(
ReplacementTransform(f1[3], f2[3]),
FadeOut(b2),
)
self.wait(duration=2)
t4 = TextMobject("That's starting to feel a bit recursive!")
t4.next_to(dg, DOWN, buff=MED_LARGE_BUFF)
self.play(FadeIn(t4))
self.wait()
code_scale = 0.75
power_code = CodeBlock(
'Java',
r"""
public static int power(int x, int n) {
if (n == 0) {
return 1;
}
int t = power(x, n - 1);
return x * t;
}
""",
code_scale=code_scale,
)
self.play(
*[FadeOut(o) for o in [t3, t4, f1[:-1], f2[3]]],
FadeInFromDown(power_code),
)
self.wait()
b1 = BraceLabel(
power_code.get_code().get_lines((2, 4)),
'Remember $x^0=1$, because math!',
brace_direction=RIGHT,
label_constructor=TextMobject,
label_scale=0.75,
)
self.play(ShowCreation(b1))
self.wait(duration=2)
t1 = TextMobject("Let's step through it to see how it goes...")
t1.next_to(power_code, DOWN)
self.play(FadeIn(t1), )
self.wait()
# Start stepping through this and see it go.
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
int y = power(4, 3);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
frame_width = 3.5
main_frame = StackFrame(main_code,
'main()',
9, ['y'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
self.play(
FadeOut(t1),
FadeOut(b1),
power_code.to_edge,
UP,
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
def call_power(x, n, call_stack):
stack_frame = StackFrame(power_code,
'power(%d, %d)' % (x, n),
1, ['x', 'n', 't'],
width=frame_width)
call_stack.animate_call(stack_frame, self)
self.play(*stack_frame.get_update_line_anims(2),
stack_frame.update_slot, 'x', x, stack_frame.update_slot,
'n', n)
if n == 0:
self.play(*stack_frame.get_update_line_anims(3))
self.wait()
call_stack.animate_return(self)
return 1
else:
self.play(*stack_frame.get_update_line_anims(5))
self.wait()
t = call_power(x, n - 1, call_stack)
self.play(
*stack_frame.get_update_line_anims(6),
stack_frame.update_slot,
't',
t,
)
self.wait()
call_stack[-1].code = power_code
call_stack.animate_return(self)
return x * t
result = call_power(4, 3, CallStack(main_frame))
self.play(*main_frame.get_update_line_anims(10),
main_frame.update_slot, 'y', result)
self.wait()
final_eq = TexMobject('4^3=', '64')
final_eq.next_to(power_code, DOWN, buff=LARGE_BUFF)
lhs = final_eq[0].copy().move_to(
main_code.get_code().get_lines(2)[12:15])
rhs = final_eq[1].copy().move_to(main_frame.slots()[0])
self.play(
ReplacementTransform(lhs, final_eq[0]),
ReplacementTransform(rhs, final_eq[1]),
)
self.wait(duration=2)
self.play(*[FadeOut(o) for o in [final_eq, main_frame, main_code]])
self.wait()
def construct(self):
# - Now, let's change this a bit and break it!
# - Now modify it (a <= 0) and call it with foo(0).
# - switch it out for the broken one, and highlight and note the change.
code_scale = 0.75
ss_good_code = CodeBlock(
'Java',
r"""
public static double StrangeSqrt(double a) {
if (a < 0) {
double b = StrangeSqrt(a * -1);
return b;
}
return Math.sqrt(a);
}
""",
code_scale=code_scale,
)
ss_good_code.to_edge(UP)
self.add(ss_good_code)
t1 = TextMobject(
"Let's break this code in a very small way and\\\\see what happens..."
)
t1.next_to(ss_good_code, DOWN, buff=LARGE_BUFF)
self.play(FadeIn(t1))
self.wait()
gl2 = ss_good_code.get_code().get_lines(2)
ghr = SurroundingRectangle(gl2[3:6])
self.play(ShowCreation(ghr))
self.wait()
ss_bad_code = CodeBlock(
'Java',
r"""
public static double StrangeSqrt(double a) {
if (a <= 0) {
double b = StrangeSqrt(a * -1);
return b;
}
return Math.sqrt(a);
}
""",
code_scale=code_scale,
)
ss_bad_code.to_edge(UP)
bl2 = ss_bad_code.get_code().get_lines(2)
bhr = SurroundingRectangle(bl2[3:7])
self.play(
ReplacementTransform(ss_good_code, ss_bad_code),
ReplacementTransform(ghr, bhr),
)
self.wait()
t2 = TextMobject(
"This small change will have a big effect on one case: 0\\\\"
"Let's run it and see.").next_to(ss_bad_code,
DOWN,
buff=LARGE_BUFF)
self.play(
FadeOut(t1),
FadeIn(t2),
)
self.wait(duration=3)
self.play(
FadeOut(t2),
FadeOut(bhr),
)
self.wait()
# - Start stepping through this and see the stack start to grow forever.
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
double n = StrangeSqrt(0);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
frame_width = 3.5
main_frame = StackFrame(main_code,
'main()',
9, ['n'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
ss_frame = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
ss_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(ss_bad_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(ss_frame, UP),
)
ss_bad_code.post_control_transfer(xi, self)
self.wait()
self.play(ss_bad_code.highlight_lines, 2, ss_frame.set_line, 2,
ss_frame.update_slot, 'a', 0)
self.wait()
self.play(ss_bad_code.highlight_lines, 3, ss_frame.set_line, 3)
self.wait()
def call_ss_again(stack_group, previous_frame, extras=None):
wait_each_step = len(stack_group) < 3
runtime = 1.0 if len(stack_group) < 2 else 0.5 if len(
stack_group) < 6 else 0.20
extra_anims = []
if len(stack_group) > 2:
extra_anims.append(
ApplyMethod(
stack_group.shift,
DOWN * previous_frame.get_height() +
DOWN * SMALL_BUFF))
if extras:
extra_anims.extend(extras)
f = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
f.next_to(previous_frame, UP, buff=SMALL_BUFF)
self.play(*extra_anims,
ss_bad_code.highlight_lines,
1,
f.set_line,
1,
FadeIn(f),
MaintainPositionRelativeTo(f, previous_frame),
run_time=runtime)
if wait_each_step:
self.wait()
self.play(ss_bad_code.highlight_lines,
2,
f.set_line,
2,
f.update_slot,
'a',
0,
run_time=runtime)
if wait_each_step:
self.wait()
self.play(ss_bad_code.highlight_lines,
3,
f.set_line,
3,
run_time=runtime)
if wait_each_step:
self.wait()
stack_group.add(f)
return f
sg = VGroup(main_frame, ss_frame)
curr_ss_frame = ss_frame
for i in range(3):
curr_ss_frame = call_ss_again(sg, curr_ss_frame)
# - When will this program end? Never?
t1 = TextMobject("Hrm... when is this going to end??").next_to(
main_code, UP, buff=LARGE_BUFF)
extra_text = [FadeIn(t1)]
for i in range(4):
curr_ss_frame = call_ss_again(sg, curr_ss_frame, extra_text)
extra_text = None
t2 = TextMobject("Never?").next_to(main_code, UP, buff=LARGE_BUFF)
extra_text = [FadeOut(t1), FadeIn(t2)]
for i in range(4):
curr_ss_frame = call_ss_again(sg, curr_ss_frame, extra_text)
extra_text = None
sg.save_state()
t3 = TextMobject("The stack is getting quite deep!").next_to(
main_code, UP, buff=LARGE_BUFF)
self.play(sg.scale, 0.20, {'about_edge': TOP}, FadeOut(t2), FadeIn(t3))
self.wait(duration=2)
self.play(sg.restore)
extra_text = [FadeOut(t3)]
for i in range(4):
curr_ss_frame = call_ss_again(sg, curr_ss_frame, extra_text)
extra_text = None
# - Well, the stack is finite, so eventually you get a SO.
# Use the Java SO exception and show it hit and stop.
so_frame = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
so_frame.slots().set_color(ORANGE)
so_frame.header_line().set_color(ORANGE)
so_frame.background_rect().set_fill(color=[BLACK, RED])
so_frame.next_to(curr_ss_frame, UP, buff=SMALL_BUFF)
so_exception = TextMobject(
'\\texttt{Exception in thread "main"\\\\java.lang.StackOverflowError}',
).set_color(YELLOW).scale(0.75).next_to(main_code, UP, buff=LARGE_BUFF)
self.play(sg.shift,
DOWN * so_frame.get_height() + DOWN * SMALL_BUFF,
ss_bad_code.get_current_highlight().set_color, ORANGE,
FadeIn(so_frame),
MaintainPositionRelativeTo(so_frame, curr_ss_frame),
Write(so_exception))
sg.add(so_frame)
self.wait(duration=2)
ss_bad_code.generate_target()
so_exception.generate_target()
ss_bad_code.target.scale(0.75)
g = VGroup(so_exception.target,
ss_bad_code.target).arrange(RIGHT, buff=LARGE_BUFF)
g.to_edge(UP)
sg.generate_target()
sg.target.scale(0.15).next_to(g, DOWN).to_edge(RIGHT)
t1 = TextMobject(
"Space for the call stack is limited,\\\\so we can't make recursive calls forever!"
)
self.play(
*[MoveToTarget(t) for t in [so_exception, ss_bad_code, sg]],
FadeOutAndShiftDown(main_code),
FadeInFromDown(t1),
)
self.wait(duration=2)
t2 = TextMobject(
"This program made {\\raise.17ex\\hbox{$\\scriptstyle\\sim$}}15,000 calls before crashing."
)
t4 = TextMobject(
"\\textit{Java SE 13.0.1 on macOS Catalina 10.15.4}").scale(0.5)
t2.next_to(t1, DOWN, buff=MED_LARGE_BUFF)
t4.to_edge(DL)
self.play(
FadeIn(t2),
FadeInFromDown(t4),
)
self.wait(duration=4)
t5 = TextMobject('\\textit{Most common mistake with recursion.}')
t6 = TextMobject("You'll see this a lot. Everyone does!")
t6.next_to(t5, DOWN, buff=LARGE_BUFF)
self.play(
*[FadeOut(t) for t in [t1, t2, t4]],
*[FadeIn(t) for t in [t5, t6]],
)
self.wait(duration=3)
# Transition
t1 = TextMobject(
"Alright, let's look at a more interesting function...")
self.play(
*[FadeOut(o) for o in self.mobjects],
FadeIn(t1),
)
self.wait()
self.play(FadeOut(t1))
self.wait()
def construct(self):
code_scale = 0.75
foo_code = CodeBlock(
'Java',
r"""
int foo() {
int n = bar(2, 1);
n += bar(2, 2);
return n;
}
""",
code_scale=code_scale,
)
bar_code = CodeBlock(
'Java',
r"""
int bar(int x, int y) {
if (x == 1) {
return y;
}
int b = bar(x - 1, y + 1);
return b;
}
""",
line_offset=5,
code_scale=code_scale,
)
main_code = CodeBlock('Java', 'off_screen')
main_code.shift(UP * 8) # Offscreen up
self.add(main_code)
title = TextMobject('CodeBlock Stepping Demo')
title.to_edge(UP)
foo_code.next_to(title, DOWN)
bar_code.next_to(foo_code.get_code(),
DOWN,
buff=MED_LARGE_BUFF,
aligned_edge=LEFT,
submobject_to_align=bar_code.get_code())
self.play(*[FadeIn(o) for o in [title, foo_code, bar_code]])
self.wait()
# Step through both code blocks until done.
xi = main_code.pre_call(foo_code, 1)
self.play(*main_code.get_control_transfer_counterclockwise(xi))
foo_code.post_control_transfer(xi, self)
foo_code.prep_annotations(2, 3)
foo_code.generate_target().highlight_lines(2).set_annotation(2, 'n: ?')
self.play(MoveToTarget(foo_code))
n = self.run_bar(bar_code, foo_code, 2, 2, 1)
self.play(foo_code.highlight_lines, 3, foo_code.set_annotation, 2,
None, foo_code.set_annotation, 3, 'n: %d' % n,
bar_code.fade_labels)
n += self.run_bar(bar_code, foo_code, 3, 2, 2)
self.play(foo_code.highlight_lines, 4, foo_code.set_annotation, 3,
'n: %d' % n)
xi = foo_code.pre_return(main_code, 1)
self.play(*foo_code.get_control_transfer_clockwise(xi))
main_code.post_control_transfer(xi, self)
self.play(FadeOut(title), FadeOut(foo_code), FadeOut(bar_code))
self.wait()
def construct(self):
title = TextMobject('The Call Stack').to_edge(UP)
t1 = TextMobject("Alright, let's do a more complicated one!")
self.add(title, t1)
self.wait()
code_scale = 0.75
main_code = CodeBlock(
'Java',
r"""
public static
void main(String[] args) {
System.out.println(foo(1));
}
""",
code_scale=code_scale,
)
# Start line: 5
foo_code = CodeBlock(
'Java',
r"""
foo(int a) {
int b = bar(a, 2);
int c = bar(a, b);
return c;
}
""",
code_scale=code_scale,
)
# Start line: 10
bar_code = CodeBlock(
'Java',
r"""
int bar(int x, int y) {
int a = x + y;
int b = a * 2;
return b;
}
""",
code_scale=code_scale,
)
cg = VGroup(main_code, foo_code, bar_code)
cg.arrange(DOWN, aligned_edge=LEFT, buff=MED_SMALL_BUFF)
cg.next_to(title, DOWN, buff=MED_SMALL_BUFF).to_edge(RIGHT)
self.play(
FadeOut(t1),
FadeInFrom(cg, RIGHT),
)
self.wait()
frame_width = 3.0
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(main_code,
'main()',
3, [('args', args_ref)],
width=frame_width)
main_frame.next_to(cg, LEFT, buff=LARGE_BUFF * 2).to_edge(DOWN)
main_code.move_hidden_highlight(3)
self.play(
FadeInFromDown(main_frame),
main_code.highlight_lines,
3,
)
self.wait()
foo_frame = StackFrame(foo_code,
'foo(1)',
5, ['a', 'b', 'c'],
width=frame_width)
foo_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(foo_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(foo_frame, UP),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 2, foo_frame.set_line, 6,
foo_frame.update_slot, 'a', 1)
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1, 2)',
10, ['x', 'y', 'a', 'b'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
xi = foo_code.pre_call(bar_code, 1)
self.play(
*foo_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(bar_frame, UP),
)
bar_code.post_control_transfer(xi, self)
self.wait()
self.play(bar_code.highlight_lines, 2, bar_frame.set_line, 11,
bar_frame.update_slot, 'x', 1, bar_frame.update_slot, 'y', 2)
self.wait()
self.play(bar_code.highlight_lines, 3, bar_frame.set_line, 12,
bar_frame.update_slot, 'a', 3)
self.wait()
self.play(bar_code.highlight_lines, 4, bar_frame.set_line, 13,
bar_frame.update_slot, 'b', 6)
self.wait()
xi = bar_code.pre_return(foo_code, 2)
self.play(
*bar_code.get_control_transfer_clockwise(xi),
Uncreate(bar_frame),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 3, foo_frame.set_line, 7,
foo_frame.update_slot, 'b', 6)
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1, 6)',
10, ['x', 'y', 'a', 'b'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
xi = foo_code.pre_call(bar_code, 1)
self.play(
*foo_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(bar_frame, UP),
)
bar_code.post_control_transfer(xi, self)
self.wait()
self.play(bar_code.highlight_lines, 2, bar_frame.set_line, 11,
bar_frame.update_slot, 'x', 1, bar_frame.update_slot, 'y', 6)
self.wait()
self.play(bar_code.highlight_lines, 3, bar_frame.set_line, 12,
bar_frame.update_slot, 'a', 7)
self.wait()
self.play(bar_code.highlight_lines, 4, bar_frame.set_line, 13,
bar_frame.update_slot, 'b', 14)
self.wait()
xi = bar_code.pre_return(foo_code, 3)
self.play(
*bar_code.get_control_transfer_clockwise(xi),
Uncreate(bar_frame),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 4, foo_frame.set_line, 8,
foo_frame.update_slot, 'c', 14)
self.wait()
xi = foo_code.pre_return(main_code, 3)
self.play(
*foo_code.get_control_transfer_clockwise(xi),
Uncreate(foo_frame),
)
main_code.post_control_transfer(xi, self)
self.wait()
def fake_frame(name):
frame_name = TextMobject(name).scale(0.75)
br = BackgroundRectangle(frame_name,
buff=SMALL_BUFF,
fill_opacity=0.15)
br.set_fill(color=[ORANGE, BLUE])
return VGroup(frame_name, br)
println_funcs = [
'BufferedWriter.write("14", 0, 2)',
'BufferedWriter(Writer).write("14")',
'PrintStream.writeln("14")',
'PrintStream.println(14)',
]
println_frames = [fake_frame(f) for f in reversed(println_funcs)]
for n, p in zip(println_frames, [main_frame] + println_frames):
n.next_to(p, UP, buff=SMALL_BUFF)
self.play(FadeInFrom(n, UP))
self.wait()
for f in reversed(println_frames):
self.play(Uncreate(f))
# self.wait()
self.play(main_code.highlight_lines, 4, main_frame.set_line, 4)
off_screen_code = CodeBlock('Java', 'off_screen')
off_screen_code.shift(UP * 8) # Offscreen up
self.add(off_screen_code)
xi = main_code.pre_return(off_screen_code, 1)
self.play(
*main_code.get_control_transfer_clockwise(xi),
Uncreate(main_frame),
)
off_screen_code.post_control_transfer(xi, self)
self.wait()
self.play(FadeOut(main_code), FadeOut(foo_code), FadeOut(bar_code))
self.wait()
def construct(self):
# Even case
ef0 = TexMobject('x^n=', 'x', '\\times', 'x \\times ... \\times x')
eb0 = BraceLabel(ef0[1:],
'$n$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ef0g = VGroup(ef0, eb0)
ef1 = TexMobject('x^n=', 'x \\times ... \\times x', '\\times',
'x \\times ... \\times x')
ef1.next_to(ef0, ORIGIN, index_of_submobject_to_align=0)
eb1n = BraceLabel(ef1[1:],
'$n$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
eb1l = BraceLabel(ef1[1:2],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
eb1r = BraceLabel(ef1[3:4],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ef2 = TexMobject('x^n=', 'x \\times ... \\times x', '\\times',
'x^{\\frac{n}{2}}')
ef2.next_to(ef0, ORIGIN, index_of_submobject_to_align=0)
eb2r = BraceLabel(ef2[3:4],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ef3 = TexMobject('x^n=', 'x^{\\frac{n}{2}}', '\\times',
'x^{\\frac{n}{2}}')
ef3.next_to(ef0, ORIGIN, index_of_submobject_to_align=0)
eb3r = BraceLabel(ef3[3:4],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
if_even = TextMobject('\\textit{if $n$ is even:}').next_to(ef0, LEFT)
self.play(ShowCreation(ef0g))
self.wait()
self.play(ReplacementTransform(ef0, ef1),
ReplacementTransform(eb0, eb1n))
self.wait()
self.play(ReplacementTransform(eb1n, eb1l), ShowCreation(eb1r),
FadeIn(if_even))
self.wait(duration=2)
self.play(ReplacementTransform(ef1, ef2),
ReplacementTransform(eb1r, eb2r))
self.wait()
self.play(ReplacementTransform(ef2, ef3), FadeOut(eb1l),
ReplacementTransform(eb2r, eb3r))
self.wait()
even_group = VGroup(if_even, ef3)
self.play(FadeOutAndShift(eb3r, UL), even_group.to_edge, UL)
self.wait()
# Prime1 eq
p1f = TexMobject('x^n=', 'x', '\\times', 'x^{n-1}')
p1t = TextMobject('From our first version, we know')
p1t.next_to(p1f, UP)
self.play(FadeIn(p1t), ShowCreation(p1f))
self.wait()
# Odd case
ot1 = TextMobject('So if $n$ is odd, then $n-1$ is even... hmm...')
ot1.next_to(p1f, UP)
self.play(ReplacementTransform(p1t, ot1))
self.wait()
of1 = TexMobject('x^n=', 'x', '\\times',
'x^{\\frac{n-1}{2}} \\times x^{\\frac{n-1}{2}}')
of1.next_to(p1f, ORIGIN, index_of_submobject_to_align=0)
self.play(ReplacementTransform(VGroup(ef3[1:]).copy(), of1[3]),
FadeOut(p1f[3]))
self.remove(*p1f[:3])
self.add(of1)
self.wait()
if_odd = TextMobject('\\textit{if $n$ is odd:}').next_to(of1[0], LEFT)
self.play(FadeOut(ot1), FadeIn(if_odd))
self.wait()
# Both
originals = [if_even, ef3, if_odd, of1]
for o in originals:
o.generate_target()
ef3.target.next_to(of1, UP, aligned_edge=LEFT)
if_even.target.next_to(ef3.target[0], LEFT)
VGroup(*[o.target for o in originals]).center().to_edge(TOP)
self.play(*[MoveToTarget(o) for o in originals])
self.wait()
eqg = VGroup(*originals)
# Simplify with int division
t1 = TextMobject(
'Fun Fact: if $n$ is odd, and we use \\texttt{int} as the datatype, then'
).next_to(eqg, DOWN, buff=LARGE_BUFF)
div_code = CodeTextString('Java',
'n / 2 == (n - 1) / 2').next_to(t1, DOWN)
self.play(FadeInFromDown(t1), FadeInFromDown(div_code))
self.wait()
of2 = TexMobject('x^n=', 'x', '\\times',
'x^{\\frac{n}{2}} \\times x^{\\frac{n}{2}}')
of2.next_to(of1, ORIGIN, index_of_submobject_to_align=0)
self.play(ReplacementTransform(div_code, of2[3]), FadeOut(of1[3]),
FadeOut(t1))
self.remove(*of1[:3])
self.add(of2)
self.wait()
originals = [if_even, ef3, if_odd, of2]
for o in originals:
o.generate_target()
for p in [ef3.target[1:], of2.target[3]]:
p.set_color(ORANGE)
eqtg = VGroup(*[o.target for o in originals]).center().to_edge(TOP)
t1 = TextMobject(
'Using \\texttt{int} for $n$ makes the equations very similar,\\\\'
'and the coding very simple!')
t1.next_to(eqtg, DOWN, buff=MED_LARGE_BUFF)
self.play(*[MoveToTarget(o) for o in originals], FadeIn(t1))
self.wait()
eqg = VGroup(*originals)
# Transform to code
code_scale = 0.7
power2_code = CodeBlock(
'Java',
r"""
public static int power2(int x, int n) {
if (n == 0) {
return 1;
}
int t = power2(x, n / 2);
if (n % 2 == 0) {
return t * t;
}
return t * t * x;
}
""",
code_scale=code_scale,
)
power2_code.to_edge(RIGHT)
ef3.generate_target()
of2.generate_target()
ef3.target.next_to(power2_code.get_code().get_lines(7),
LEFT,
buff=LARGE_BUFF)
of2.target.next_to(power2_code.get_code().get_lines(9),
LEFT,
buff=LARGE_BUFF)
ef3.target.next_to(of2.target,
UP,
aligned_edge=RIGHT,
coor_mask=X_AXIS)
et = TextMobject('\\textit{even:}')
ot = TextMobject('\\textit{odd:}')
ot.next_to(of2.target[0], LEFT)
et.next_to(ef3.target[0], LEFT)
self.play(FadeOut(t1))
self.play(
FadeOut(if_even),
FadeOut(if_odd),
FadeInFrom(power2_code, RIGHT),
MoveToTarget(ef3),
MoveToTarget(of2),
ReplacementTransform(if_even, et),
ReplacementTransform(if_odd, ot),
)
self.wait()
recursive_call_hr = SurroundingRectangle(
power2_code.get_code().get_lines(5)[5:-1])
xn2_hr = SurroundingRectangle(ef3[-1])
ec_hr = SurroundingRectangle(
power2_code.get_code().get_lines(7)[-4:-1])
ef_hr = SurroundingRectangle(ef3[1:])
oc_hr = SurroundingRectangle(
power2_code.get_code().get_lines(9)[-6:-1])
of_hr = SurroundingRectangle(of2[1:])
for f, c in [(xn2_hr, recursive_call_hr), (ef_hr, ec_hr),
(of_hr, oc_hr)]:
self.play(ShowCreation(f), ShowCreation(c))
self.wait()
self.play(Uncreate(f), Uncreate(c))
self.wait()
def construct(self):
t1 = TextMobject("Let's go back to our original equation").shift(UP)
self.play(FadeInFromDown(t1))
self.wait()
# Even case
ef1 = TexMobject('x^n=', 'x \\times ... \\times x', '\\times',
'x \\times ... \\times x')
eb1n = BraceLabel(ef1[1:],
'$n$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
eb1l = BraceLabel(ef1[1:2],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
eb1r = BraceLabel(ef1[3:4],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ef3 = TexMobject('x^n=', 'x^{\\frac{n}{2}}', '\\times', 'x',
'^{\\frac{n}{2}}')
ef3.next_to(ef1, ORIGIN, index_of_submobject_to_align=0)
eb3l = BraceLabel(ef3[1:2],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
if_even = TextMobject('\\textit{if $n$ is even:}').next_to(
ef1, LEFT).set_color(YELLOW)
self.play(ShowCreation(ef1), ShowCreation(eb1n), t1.shift, UP)
self.wait(duration=2)
self.play(ReplacementTransform(eb1n, eb1l), ShowCreation(eb1r),
FadeIn(if_even), FadeOut(t1))
self.wait(duration=2)
self.play(ReplacementTransform(ef1[1], ef3[1]),
ReplacementTransform(eb1l, eb3l))
self.wait()
tmp_ef3_right = VGroup(ef3[2].copy(), ef3[3].copy(), ef3[4].copy())
tmp_ef3_right.next_to(ef1[2],
ORIGIN,
submobject_to_align=tmp_ef3_right[0])
eb3r = BraceLabel(tmp_ef3_right[1:],
'$\\frac{n}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
self.play(ReplacementTransform(ef1[3:], tmp_ef3_right[1:]),
ReplacementTransform(eb1r, eb3r))
self.wait()
self.play(
ReplacementTransform(ef1[2], ef3[2]),
ReplacementTransform(tmp_ef3_right[1:], ef3[3:]),
FadeOutAndShift(eb3r, LEFT),
FadeOut(eb3l),
)
self.remove(ef1[0])
self.add(ef3)
self.wait()
even_group = VGroup(if_even, ef3)
self.play(even_group.to_edge, UL)
self.wait()
# Odd case
ot1 = TextMobject(
"Now, let's figure out what to do if $n$ is odd").shift(
UP * 2).set_color(BLUE)
self.play(FadeInFromDown(ot1))
of1 = TexMobject('x^n=', 'x \\times ... \\times x', '\\times',
'x \\times ... \\times x', '\\times x')
ob1n = BraceLabel(of1[1:],
'$n$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ob1nm1 = BraceLabel(of1[1:-1],
'$n-1$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ob1l = BraceLabel(of1[1:2],
'$\\frac{n-1}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
ob1r = BraceLabel(of1[3:4],
'$\\frac{n-1}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
of3 = TexMobject('x^n=', 'x', '^{\\frac{n-1}{2}}', '\\times', 'x',
'^{\\frac{n-1}{2}}', '\\times x')
of3.next_to(of1, ORIGIN, index_of_submobject_to_align=0)
ob3l = BraceLabel(of3[1:3],
'$\\frac{n-1}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
if_odd = TextMobject('\\textit{if $n$ is odd:}').next_to(
of1, LEFT).set_color(YELLOW)
self.play(ShowCreation(of1), ShowCreation(ob1n))
self.wait(duration=2)
self.play(ReplacementTransform(ob1n, ob1nm1), FadeIn(if_odd),
FadeOut(ot1))
self.wait(duration=2)
self.play(ReplacementTransform(ob1nm1, ob1l), ShowCreation(ob1r))
self.wait(duration=2)
self.play(ReplacementTransform(of1[1], of3[1:3]),
ReplacementTransform(ob1l, ob3l))
self.wait()
tmp_of3_right = VGroup(of3[3].copy(), of3[4].copy(), of3[5].copy())
tmp_of3_right.next_to(of1[2],
ORIGIN,
submobject_to_align=tmp_of3_right[0])
ob3r = BraceLabel(tmp_of3_right[1:],
'$\\frac{n-1}{2}$ \\textit{times}',
brace_direction=UP,
label_constructor=TextMobject)
self.play(ReplacementTransform(of1[3], tmp_of3_right[1:]),
ReplacementTransform(ob1r, ob3r))
self.wait()
self.play(
ReplacementTransform(of1[2], of3[3]),
ReplacementTransform(tmp_of3_right[1:], of3[4:6]),
ReplacementTransform(of1[4], of3[-1]),
FadeOutAndShift(ob3r, LEFT),
FadeOut(ob3l),
)
self.remove(of1[0])
self.add(of3)
self.wait()
# Both
originals = [if_even, ef3, if_odd, of3]
for o in originals:
o.generate_target()
ef3.target.next_to(of3, UP, aligned_edge=LEFT)
if_even.target.next_to(ef3.target[0], LEFT)
VGroup(*[o.target for o in originals]).center().to_edge(TOP)
self.play(*[MoveToTarget(o) for o in originals])
self.wait()
eqg = VGroup(*originals)
# Simplify with int division
t1 = TextMobject(
'Fun Fact: if $n$ is odd, and we use \\texttt{int} as the datatype, then',
tex_to_color_map={
'int': RED
}).next_to(eqg, DOWN, buff=LARGE_BUFF)
div_code = CodeTextString('Java', '(n-1)/2 == n/2').next_to(t1, DOWN)
self.play(FadeInFromDown(t1), FadeInFromDown(div_code))
self.wait(duration=3)
t2 = TextMobject('Integer division \\textit{truncates}: '
'\\texttt{5/2 == 2}'
', \\textit{not} '
'\\texttt{2.5}')
t2.next_to(div_code, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromDown(t2))
self.wait(duration=3)
# Indicate movement before each exp transformation from code
of4 = TexMobject('x^n=', 'x', '^{\\frac{n}{2}}', '\\times', 'x',
'^{\\frac{n}{2}}', '\\times x')
of4.next_to(of3, ORIGIN, index_of_submobject_to_align=0)
def highlight_and_switch_exp(target_exp, old_exp):
hrc = SurroundingRectangle(div_code[0][:7])
hrf = SurroundingRectangle(old_exp)
self.play(ShowCreation(hrc), ShowCreation(hrf))
self.wait()
self.play(Uncreate(hrc), Uncreate(hrf))
self.play(Indicate(div_code[0][-3:]))
self.play(
ReplacementTransform(div_code[0][-3:].copy(), target_exp),
FadeOut(old_exp))
highlight_and_switch_exp(of4[2], of3[2])
tmp_of4_right = VGroup(of4[4].copy(), of4[5].copy())
tmp_of4_right.next_to(of3[4],
ORIGIN,
submobject_to_align=tmp_of4_right[0])
highlight_and_switch_exp(tmp_of4_right[1], of3[5])
self.wait()
self.play(
ReplacementTransform(of3[3:5], of4[3:5]),
ReplacementTransform(tmp_of4_right[1], of4[5]),
ReplacementTransform(of3[-1], of4[-1]),
)
self.remove(*of3)
self.add(of4)
self.wait()
self.play(*[FadeOut(o) for o in [t1, t2, div_code]])
originals = [if_even, ef3, if_odd, of4]
for o in originals:
o.generate_target()
for p in [ef3.target[1:], of4.target[1:6]]:
p.set_color(ORANGE)
eqtg = VGroup(*[o.target for o in originals]).center().to_edge(TOP)
t1 = TextMobject(
'Using \\texttt{int} for $n$ makes the equations very similar,\\\\'
'and the coding very simple!',
tex_to_color_map={'int': RED})
t1.next_to(eqtg, DOWN, buff=MED_LARGE_BUFF)
self.play(*[MoveToTarget(o) for o in originals], FadeIn(t1))
self.wait(duration=3)
eqg = VGroup(*originals)
# Transform to code
code_scale = 0.7
power2_code = CodeBlock(
'Java',
r"""
public static int power2(int x, int n) {
if (n == 0) {
return 1;
}
int t = power2(x, n / 2);
if (n % 2 == 0) {
return t * t;
}
return t * t * x;
}
""",
code_scale=code_scale,
)
power2_code.to_edge(RIGHT)
ef3.generate_target()
of4.generate_target()
ef3.target.next_to(power2_code.get_code().get_lines(7),
LEFT,
buff=LARGE_BUFF)
of4.target.next_to(power2_code.get_code().get_lines(9),
LEFT,
buff=LARGE_BUFF)
ef3.target.next_to(of4.target,
UP,
index_of_submobject_to_align=0,
coor_mask=X_AXIS)
et = TextMobject('\\textit{even:}')
ot = TextMobject('\\textit{odd:}')
ot.next_to(of4.target[0], LEFT)
et.next_to(ef3.target[0], LEFT)
self.play(FadeOut(t1))
self.play(
FadeOut(if_even),
FadeOut(if_odd),
FadeInFrom(power2_code, RIGHT),
MoveToTarget(ef3),
MoveToTarget(of4),
ReplacementTransform(if_even, et),
ReplacementTransform(if_odd, ot),
)
self.wait()
highlights = [
[
SurroundingRectangle(
power2_code.get_code().get_lines(1)[-6:-2]),
SurroundingRectangle(
power2_code.get_code().get_lines(5)[-5:-2]),
SurroundingRectangle(ef3[-1]),
],
[
SurroundingRectangle(
power2_code.get_code().get_lines(5)[5:-1]),
SurroundingRectangle(ef3[-2:]),
],
[
SurroundingRectangle(
power2_code.get_code().get_lines(7)[-4:-1]),
SurroundingRectangle(ef3[1:]),
],
[
SurroundingRectangle(
power2_code.get_code().get_lines(9)[-6:-1]),
SurroundingRectangle(of4[1:]),
],
]
for g in highlights:
self.play(*[ShowCreation(h) for h in g])
self.wait(duration=1.5)
self.play(*[Uncreate(h) for h in g])
self.wait()
self.play(*[FadeOut(o) for o in self.mobjects if o != power2_code])
power2_code.generate_target()
power2_code.target.center()
power2_code.target.to_edge(UP)
self.play(MoveToTarget(power2_code))
def construct(self):
code_scale = 0.7
power2_code = CodeBlock(
'Java',
r"""
public static int power2(int x, int n) {
if (n == 0) {
return 1;
}
int t = power2(x, n / 2);
if (n % 2 == 0) {
return t * t;
}
return t * t * x;
}
""",
code_scale=code_scale,
)
power2_code.to_edge(UP)
self.add(power2_code)
t1 = TextMobject(
"This version should call itself fewer than $n$ times")
t1.next_to(power2_code, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromDown(t1))
self.wait(duration=2.5)
t2 = TextMobject(
'How many times do you think \\texttt{power2(2,30)} will call itself?',
tex_to_color_map={'30': YELLOW})
t2.next_to(t1, ORIGIN)
self.play(FadeOutAndShift(t1, UP), FadeInFromDown(t2))
self.wait(duration=2)
t3 = TextMobject("We know it'll be less than 30! Maybe 15?")
t3.next_to(t2, DOWN, buff=MED_LARGE_BUFF)
self.play(FadeInFromDown(t3))
self.wait(duration=2)
t4 = TextMobject("How about a lot less? Let's see...")
t4.next_to(t3, ORIGIN)
self.play(ReplacementTransform(t3, t4))
self.wait(duration=2)
self.play(*[FadeOut(o) for o in self.mobjects if o != power2_code])
# Start stepping through this and see it go.
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
int y = power2(2, 30);
}
""",
line_offset=10,
code_scale=code_scale - 0.1,
)
frame_width = 3.5
main_frame = StackFrame(main_code,
'main()',
12, ['y'],
width=frame_width,
slot_char_width=8)
main_code.highlight_lines(12)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
def call_power2(x, n, call_stack, cc_num):
new_cc_num = TextMobject(str(len(call_stack) -
1)).move_to(cc_num).set_color(YELLOW)
update_cc_anims = [ReplacementTransform(cc_num, new_cc_num)]
call_ret_delay = 0.5
stack_frame = StackFrame(power2_code,
'power(%d, %d)' % (x, n),
1, ['x', 'n', 't'],
width=frame_width)
call_stack.animate_call(stack_frame,
self,
extra_anims=update_cc_anims)
self.play(
*stack_frame.get_update_line_anims(2),
stack_frame.update_slot,
'x',
x,
stack_frame.update_slot,
'n',
n,
)
if n == 0:
self.play(*stack_frame.get_update_line_anims(3))
self.wait(duration=call_ret_delay)
call_stack.animate_return(self)
return 1
else:
self.play(*stack_frame.get_update_line_anims(5))
self.wait(duration=call_ret_delay)
t = call_power2(x, n // 2, call_stack, new_cc_num)
self.play(
*stack_frame.get_update_line_anims(6),
stack_frame.update_slot,
't',
t,
)
if n % 2 == 0:
self.play(*stack_frame.get_update_line_anims(7))
self.wait(duration=call_ret_delay)
call_stack.animate_return(self)
return t * t
self.play(*stack_frame.get_update_line_anims(9))
self.wait(duration=call_ret_delay)
call_stack.animate_return(self)
return t * t * x
cc_label = TextMobject('Recursive Calls').scale(0.75)
cc_label.to_edge(UL).shift(DOWN)
call_counter = TextMobject('0').set_color(YELLOW).next_to(
cc_label, DOWN)
self.play(FadeIn(call_counter), FadeIn(cc_label))
result = call_power2(2, 30, CallStack(main_frame), call_counter)
self.play(
*main_frame.get_update_line_anims(13),
main_frame.update_slot,
'y',
result,
)
self.wait()
t1 = TextMobject(
'We got our answer in just 5 recursive calls!').set_color(YELLOW)
t1.next_to(power2_code, DOWN, buff=MED_LARGE_BUFF)
self.play(ShowCreation(t1))
self.wait(duration=2)
t1.generate_target()
t1.target.center().to_edge(TOP)
t2 = TextMobject('But why?').next_to(t1.target, DOWN, buff=LARGE_BUFF)
self.play(
MoveToTarget(t1),
FadeInFromDown(t2),
*[FadeOut(o) for o in self.mobjects if o != t1],
)
def construct(self):
title = TextMobject('Quick Review: The Call Stack').to_edge(UP)
code_scale = 0.75
main_code = CodeBlock(
'Java',
r"""
public static
void main(String[] args) {
int n = foo(2);
}
""",
code_scale=code_scale,
)
foo_code = CodeBlock(
'Java',
r"""
static int foo(int x) {
int n = bar(x + 1, x * 2);
return n;
}
""",
code_scale=code_scale,
)
bar_code = CodeBlock(
'Java',
r"""
static int bar(int x,
int y) {
int a = x + y;
return a;
}
""",
code_scale=code_scale,
)
fbg = VGroup(main_code, foo_code, bar_code)
fbg.arrange(DOWN, buff=MED_SMALL_BUFF, aligned_edge=LEFT)
fbg.to_edge(DR)
self.play(
ShowCreation(title),
FadeInFrom(fbg, RIGHT),
)
self.wait()
frame_width = 3.0
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(main_code,
'main()',
3, [('args', args_ref), 'n'],
width=frame_width)
main_frame.next_to(fbg, LEFT, buff=LARGE_BUFF).to_edge(DOWN)
main_code.move_highlight_rect(3)
text_scale = 0.75
b1 = BraceLabel(main_frame,
'The call stack\\\\starts with main()',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
self.play(
FadeInFrom(main_frame, UP),
main_code.highlight_lines,
3,
FadeInFrom(b1, UP),
)
self.wait()
foo_frame = StackFrame(foo_code,
'foo(2)',
5, ['x', 'n'],
width=frame_width)
foo_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
b2 = BraceLabel(foo_frame,
'Calls push frames',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
hr_caller, hr_callee = main_code.setup_for_call(foo_code, 1)
self.play(
main_code.highlight_caller,
ReplacementTransform(hr_caller, hr_callee, path_arc=np.pi),
FadeInFrom(foo_frame, UP),
FadeInFrom(b2, UP),
)
foo_code.complete_callee(hr_callee, self)
self.wait()
self.play(
foo_code.highlight_lines,
2,
foo_frame.set_line,
6,
foo_frame.update_slot,
'x',
2,
)
self.wait()
bar_frame = StackFrame(bar_code,
'bar(3, 4)',
10, ['x', 'y', 'a'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
b3 = BraceLabel(bar_frame,
'Holds arguments\\\\and locals',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
hr_caller, hr_callee = foo_code.setup_for_call(bar_code, (1, 2))
self.play(
foo_code.highlight_caller,
ReplacementTransform(hr_caller, hr_callee, path_arc=np.pi),
FadeInFrom(bar_frame, UP),
FadeInFrom(b3, UP),
)
bar_code.complete_callee(hr_callee, self)
self.wait()
self.play(
bar_code.highlight_lines,
3,
bar_frame.set_line,
11,
bar_frame.update_slot,
'x',
3,
bar_frame.update_slot,
'y',
4,
)
self.wait()
self.play(
bar_code.highlight_lines,
4,
bar_frame.set_line,
12,
bar_frame.update_slot,
'a',
7,
)
self.wait(duration=3)
hr_returner, hr_returnee = bar_code.setup_for_return(foo_code)
self.play(
ReplacementTransform(hr_returner, hr_returnee, path_arc=-np.pi),
foo_code.highlight_returnee,
Uncreate(bar_frame),
FadeOutAndShift(b3, LEFT),
FadeOutAndShift(b2, LEFT),
FadeOutAndShift(b1, LEFT),
)
foo_code.complete_returnee(hr_returnee, self)
self.wait()
b4 = BraceLabel(foo_frame,
'Returns pop',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
self.play(
foo_code.highlight_lines,
3,
foo_frame.set_line,
7,
foo_frame.update_slot,
'n',
7,
ShowCreation(b4),
)
self.wait()
hr_returner, hr_returnee = foo_code.setup_for_return(main_code)
self.play(
ReplacementTransform(hr_returner, hr_returnee, path_arc=-np.pi),
main_code.highlight_returnee,
Uncreate(foo_frame),
FadeOutAndShift(b4, LEFT),
)
main_code.complete_returnee(hr_returnee, self)
self.wait()
self.play(
main_code.highlight_lines,
4,
main_frame.set_line,
4,
main_frame.update_slot,
'n',
7,
)
self.wait()
hr_returner, hr_returnee = main_code.setup_for_return(main_code)
hr_returnee.shift(UP * 4)
self.play(
ReplacementTransform(hr_returner, hr_returnee, path_arc=-np.pi),
Uncreate(main_frame),
)
self.remove(hr_returnee)
self.wait()
t1 = TextMobject('Take a moment to think about\\\\'
'where args and locals live,\\\\'
'and what the call stack looks like.').to_edge(LEFT)
t2 = TextMobject('\\textit{It will help later!!}').next_to(
t1, DOWN, buff=LARGE_BUFF)
self.play(FadeIn(t1))
self.wait()
self.play(ShowCreation(t2))
self.wait(duration=2)
def construct(self):
title = TextMobject('The Call Stack').to_edge(UP)
self.add(title)
frame_width = 3.0
dummy_code = CodeBlock('Java', 'foo')
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(dummy_code,
'main()',
3, [('args', args_ref)],
width=frame_width)
foo_frame = StackFrame(dummy_code,
'foo()',
6, [('n', 6)],
width=frame_width)
bar_frame = StackFrame(dummy_code,
'bar(1, 2)',
13, [('x', 1), ('y', 2), ('a', 3), ('b', 6)],
width=frame_width)
main_frame.to_edge(DOWN)
foo_frame.next_to(main_frame, UP)
bar_frame.next_to(foo_frame, UP)
frame_group = VGroup(main_frame, foo_frame, bar_frame)
self.play(
LaggedStartMap(FadeInFrom,
frame_group,
group=frame_group,
direction=UP,
lag_ratio=0.5))
self.wait()
text_scale = 0.75
b1 = BraceLabel(main_frame,
'Always starts\\\\with main()',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
# b2 = BraceLabel(foo_frame, ['Calls push frames,\\\\', 'returns pop'],
# brace_direction=RIGHT, label_constructor=TextMobject,
# alignment='')
b3 = BraceLabel(bar_frame.slots()[0:2],
'Parameters',
brace_direction=RIGHT,
label_constructor=TextMobject,
label_scale=text_scale)
b4 = BraceLabel(bar_frame.slots()[2:4],
'Locals',
brace_direction=RIGHT,
label_constructor=TextMobject,
label_scale=text_scale)
b5 = BraceLabel(bar_frame.slots()[0:4],
'Storage for all\\\\variables in a function',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
notes = VGroup(b1, b5, b3, b4)
box_count = 8
colors = color_gradient([BLUE, ORANGE], box_count)
little_boxes = VGroup(*[
Rectangle(height=0.25, width=0.75, fill_opacity=1, color=colors[i])
for i in range(box_count)
])
little_boxes.arrange(UP, buff=0.1)
push_up = TextMobject('Calls push\\\\frames').scale(text_scale)
push_up.next_to(little_boxes, DOWN)
pua = Arrow(push_up.get_bottom(), push_up.get_top()).scale(2)
pua.next_to(push_up, LEFT)
pug = VGroup(push_up, pua)
pop_down = TextMobject('Returns pop\\\\frames').scale(text_scale)
pop_down.next_to(little_boxes, UP)
pda = Arrow(pop_down.get_top(), pop_down.get_bottom()).scale(2)
pda.next_to(pop_down, RIGHT)
pdg = VGroup(pop_down, pda)
bg = VGroup(little_boxes, pug, pdg)
bg.to_edge(RIGHT, buff=MED_LARGE_BUFF)
self.play(
LaggedStartMap(ShowCreation,
notes,
group=notes,
lag_ratio=0.7,
run_time=3.0))
self.play(
FadeIn(pug),
LaggedStartMap(FadeInFrom,
little_boxes,
lambda m: (m, RIGHT),
lag_ratio=1.0,
run_time=3.0))
self.play(FadeIn(pdg))
pdg.generate_target()
pdg.target.next_to(little_boxes[3], UP,
submobject_to_align=pdg[0]).set_opacity(1.0)
self.play(
MoveToTarget(pdg, run_time=3.0),
LaggedStartMap(FadeOutAndShift,
VGroup(*list(reversed(little_boxes))[:4]),
lambda m: (m, RIGHT),
lag_ratio=1.0,
run_time=2.0),
)
self.wait(duration=5)
end_scale_group = VGroup(*self.mobjects)
end_fade_group = VGroup(title)
self.animate_yt_end_screen(end_scale_group,
end_fade_group,
show_elements=False,
show_rects=False)
def construct(self):
f0 = TexMobject("F_0 = 0")
f1 = TexMobject("F_1 = 1")
fn = TexMobject("F_n = F_{n-1} + F_{n-2}")
fg = VGroup(f0, f1, fn)
fg.arrange(RIGHT, buff=LARGE_BUFF).shift(UP)
self.add(fg)
fib_small_code = CodeBlock(
'Java',
r"""
public static int fib(int n) {
if (n == 0) {
return 0;
}
if (n == 1) {
return 1;
}
return fib(n - 1) + fib(n - 2);
}
""",
)
fib_code = CodeBlock(
'Java',
r"""
public static int fib(int n) {
if (n == 0) {
return 0;
}
if (n == 1) {
return 1;
}
int fn1 = fib(n - 1);
int fn2 = fib(n - 2);
return fn1 + fn2;
}
""",
)
fib_small_code.to_edge(RIGHT)
f0.generate_target()
f1.generate_target()
fn.generate_target()
fsc = fib_small_code.get_code()
eq_code_buff = LARGE_BUFF * 1.5
f0.target.next_to(fsc.get_lines((2, 5)), LEFT, buff=eq_code_buff)
f1.target.next_to(fsc.get_lines((5, 8)), LEFT, buff=eq_code_buff)
fn.target.next_to(fsc.get_lines(8), LEFT, buff=eq_code_buff)
self.play(*[MoveToTarget(o) for o in [f0, f1, fn]], )
self.play(FadeInFrom(fib_small_code, RIGHT), )
self.wait(duration=3)
fib_small_code.generate_target()
fib_small_code.target.move_to(fib_code, aligned_edge=UL)
self.play(FadeOut(VGroup(f0, f1, fn)), MoveToTarget(fib_small_code))
adj_desc = TextMobject(
"Let's make this a little easier to trace through...")
adj_desc.to_edge(DOWN)
self.play(FadeIn(adj_desc))
self.wait()
fc = fib_code.get_code()
self.play(
fsc[-2].next_to,
fc[-2],
{
'direction': ORIGIN,
'index_of_submobject_to_align': 0,
},
fsc[-1].move_to,
fc[-1],
{'aligned_edge': LEFT},
)
# 012 345 6 78901 2 345
# int fn1 = fib(n - 1);
self.play(FadeIn(fc[-4][:7]), )
# 012345 67890 1 23 4 56789 0 123
# return fib(n - 1) + fib(n - 2);
self.play(
fsc[-2][6:14].move_to,
fc[-4][7:15],
)
# 012345 678 9 0123
# return fn1 + fn2;
self.play(
FadeIn(fc[-4][-1]),
FadeIn(fc[-2][6:9]),
fsc[-2][14].move_to,
fc[-2][9],
)
self.play(FadeIn(fc[-3][:7]), )
self.play(
fsc[-2][15:23].move_to,
fc[-3][7:15],
)
self.play(
FadeIn(fc[-3][-1]),
FadeIn(fc[-2][10:13]),
fsc[-2][-1].move_to,
fc[-2][-1],
)
self.clear()
self.add(fib_code, adj_desc)
self.wait()
t1 = TextMobject("Okay, let's run it")
t1.move_to(adj_desc)
self.play(ReplacementTransform(adj_desc, t1))
self.wait(duration=2)
self.play(FadeOut(t1))
def construct(self):
unsorted = [11, 0, 8, 2, 2, 9, 14, 5]
code_scale = 0.6
# TODO: move to base, since it references code lines and runs this code
ms_code = CodeBlock(
'Java',
r"""
public static int[] mergeSort(int[] a) {
if (a.length == 1) {
return a;
}
int m = a.length / 2;
int[] l, r;
l = Arrays.copyOfRange(a, 0, m);
r = Arrays.copyOfRange(a, m, a.length);
l = mergeSort(l);
r = mergeSort(r);
return merge(l, r);
}
""",
code_scale=code_scale,
)
ms_code.set_annotation(5, None)
t1 = TextMobject("Recursive mergesort in Java")
t1.to_edge(UP)
ms_code.next_to(t1, DOWN, buff=MED_LARGE_BUFF)
self.play(FadeIn(t1))
self.play(
LaggedStartMap(FadeInFromDown, ms_code.get_code(), lag_ratio=0.2))
self.wait(duration=3.0)
t2 = TextMobject(
"Let's trace through this and track our work with a tree",
buff=LARGE_BUFF)
t2.next_to(ms_code, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromDown(t2))
self.wait(duration=3)
self.play(ms_code.to_edge, DR, FadeOutAndShiftDown(t2),
FadeOutAndShift(t1, UP))
colors = color_gradient([PINK, BLUE, YELLOW_D], 15)
tree = build_merge_sort_tree(unsorted, text_scale=1.0)
update_tree_colors(tree, colors)
tree.layout(1.6, 1.2)
g = tree.to_vgroup()
g.center().to_edge(UP)
be = Merge8Exposition(self, tree, ms_code)
t1 = TextMobject("Start with an array of random numbers")
t1.next_to(tree.label, DOWN, buff=MED_LARGE_BUFF)
be.deferred_play(1, FadeIn(t1))
be.deferred_wait(1)
be.deferred_play(3, FadeOut(t1))
be.play(FadeIn(tree.label))
self.run_merge_sort(tree, be, 0)
self.wait()
t1 = TextMobject("We divide the problem on the way down")
t2 = TextMobject("and we recombine by merging on the way up")
t1.shift(DOWN * 1.5)
t2.next_to(t1, DOWN)
self.play(FadeInFromDown(t1))
self.wait()
self.play(FadeInFromDown(t2))
self.wait(duration=3)
t3 = TextMobject("We call this \\textit{divide-and-conquer}")
t4 = TextMobject("\\textit{This is very common!} You'll see it a lot.")
t3.shift(DOWN * 1.5)
t4.next_to(t3, DOWN)
self.play(FadeOutAndShiftDown(t1), FadeOutAndShiftDown(t2))
self.play(FadeInFromDown(t3))
self.wait()
self.play(FadeInFromDown(t4))
self.wait(duration=3)
t5 = TextMobject("This one was nicely balanced and even...")
t6 = TextMobject("let's try one that's a little bit odd")
t5.shift(DOWN * 1.5)
t6.next_to(t5, DOWN)
self.play(FadeOutAndShiftDown(t3), FadeOutAndShiftDown(t4))
self.play(FadeInFromDown(t5))
self.wait()
self.play(FadeInFromDown(t6))
self.wait(duration=3)
self.play(*[FadeOut(o) for o in self.mobjects])
def construct(self):
fib_code = CodeBlock(
'Java',
r"""
public static int fib(int n) {
if (n == 0) {
return 0;
}
if (n == 1) {
return 1;
}
int fn1 = fib(n - 1);
int fn2 = fib(n - 2);
return fn1 + fn2;
}
""",
)
self.add(fib_code)
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
int x = fib(3);
}
""",
line_offset=11,
code_scale=0.6,
)
frame_width = 2.5
main_frame = StackFrame(main_code,
'main()',
13, ['x'],
width=frame_width)
main_code.highlight_lines(13)
VGroup(main_code,
main_frame).arrange(RIGHT, buff=LARGE_BUFF * 2).to_edge(DOWN)
self.play(
fib_code.to_edge,
UP,
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
def call_fib(run_ctx, n, call_stack):
run_ctx['call_count'] += 1
call_ret_delay = 0.5
stack_frame = StackFrame(fib_code,
'fib(%d)' % n,
1, ['n', 'fn1', 'fn2'],
width=frame_width)
call_stack.animate_call(stack_frame, self)
self.play(
*stack_frame.get_update_line_anims(2),
stack_frame.update_slot,
'n',
n,
)
if n == 0:
self.play(*stack_frame.get_update_line_anims(3))
self.wait(duration=call_ret_delay)
call_stack.animate_return(self)
return 0
self.play(*stack_frame.get_update_line_anims(5))
if n == 1:
self.play(*stack_frame.get_update_line_anims(6))
self.wait(duration=call_ret_delay)
call_stack.animate_return(self)
return 1
self.play(*stack_frame.get_update_line_anims(8))
self.wait(duration=call_ret_delay)
fn1 = call_fib(run_ctx, n - 1, call_stack)
self.play(
*stack_frame.get_update_line_anims(9),
stack_frame.update_slot,
'fn1',
fn1,
)
if run_ctx['call_count'] == 4:
t1 = TextMobject('\\textit{Whoa!!}')
t1.set_color(YELLOW).scale(1.2)
t1.next_to(fib_code, LEFT, buff=MED_LARGE_BUFF)
self.play(GrowFromCenter(t1))
t2 = TextMobject("\\textit{I'm lost...}")
t2.next_to(t1, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromPoint(t2, t2.get_center()))
run_ctx['whoa_desc'] = VGroup(t1, t2)
self.wait(duration=call_ret_delay)
fn2 = call_fib(run_ctx, n - 2, call_stack)
self.play(
*stack_frame.get_update_line_anims(10),
stack_frame.update_slot,
'fn2',
fn2,
)
self.wait(duration=call_ret_delay)
call_stack.animate_return(self)
return fn1 + fn2
run_ctx = {
'call_count': 0,
}
result = call_fib(run_ctx, 3, CallStack(main_frame))
self.play(
*main_frame.get_update_line_anims(14),
main_frame.update_slot,
'x',
result,
)
self.wait(duration=2)
hrm_desc = TextMobject(
"That worked, but it was really hard to follow!")
hrm_desc.next_to(fib_code, DOWN, buff=MED_LARGE_BUFF)
self.play(FadeOutAndShiftDown(main_frame),
FadeOutAndShiftDown(main_code),
FadeOut(run_ctx['whoa_desc']))
self.play(FadeInFromDown(hrm_desc))
self.wait(duration=2.5)
t1 = TextMobject("The call stack shows where we are at any moment")
t1.move_to(hrm_desc)
t2 = TextMobject("but we don't know where we've been...")
t2.next_to(t1, DOWN)
t3 = TextMobject("or where we're going...")
t3.next_to(t2, DOWN)
self.play(ReplacementTransform(hrm_desc, t1))
self.wait(duration=2)
self.play(FadeInFromDown(t2))
self.wait(duration=2)
self.play(FadeInFromDown(t3))
self.wait(duration=2)
t4 = TextMobject(
"Let's go again, but draw a new picture along the way")
t4.move_to(t1)
self.play(*[FadeOutAndShift(o, UP) for o in [t1, t2, t3]],
FadeInFromDown(t4))
self.wait(duration=2.5)
self.play(FadeOut(t4))
def construct(self):
code_scale = 0.75
foo_code = CodeBlock(
'Java',
r"""
int foo() {
int n = bar(2, 1);
n += bar(2, 2);
return n;
}
""",
add_labels=True,
code_scale=code_scale,
)
bar_code = CodeBlock(
'Java',
r"""
int bar(int x, int y) {
if (x == 1) {
return y;
}
int b = bar(x - 1, y + 1);
return b;
}
""",
line_offset=5,
add_labels=True,
code_scale=code_scale,
)
title = TextMobject('CodeBlock Basics Demo')
title.to_edge(UP)
foo_code.next_to(title, DOWN)
foo_code.fade_labels()
bar_code.next_to(foo_code.get_code(),
DOWN,
buff=MED_LARGE_BUFF,
aligned_edge=LEFT,
submobject_to_align=bar_code.get_code())
self.play(*[FadeIn(o) for o in [title, foo_code, bar_code]])
self.wait(0.5)
self.play(foo_code.highlight_lines, 1, bar_code.highlight_lines,
(6, 8))
self.wait(0.5)
self.play(foo_code.highlight_lines, 2, bar_code.highlight_lines,
(8, 10))
self.play(foo_code.highlight_lines, 3, bar_code.highlight_lines,
(10, 12))
self.wait(0.5)
self.play(Indicate(foo_code))
self.wait(0.5)
self.play(Indicate(bar_code))
self.wait(0.5)
self.play(foo_code.remove_highlight, bar_code.remove_highlight)
self.wait(0.5)
self.play(FadeOut(foo_code))
self.wait(0.5)
self.play(FadeIn(foo_code))
self.wait(0.5)
self.play(foo_code.show_labels, bar_code.fade_labels)
self.wait(0.5)
self.play(foo_code.fade_labels, bar_code.show_labels)
self.wait(0.5)
foo_code.move_hidden_highlight(2)
bar_code.move_hidden_highlight((8, 10))
self.wait(0.5)
self.play(foo_code.highlight_lines, 2, bar_code.highlight_lines,
(8, 10))
self.wait(0.5)
self.play(foo_code.highlight_lines, 4, bar_code.highlight_lines,
(6, 9))
self.wait(0.5)
self.play(foo_code.remove_highlight, bar_code.remove_highlight)
self.wait(0.5)
self.play(FadeOut(foo_code), FadeOut(bar_code))
self.wait()
def construct(self):
fib_code = self.get_fib_code(0.75)
fib_code.to_edge(UP)
self.add(fib_code)
fc2 = self.get_fib_code(0.6)
fc2.to_edge(UR)
self.play(ReplacementTransform(fib_code, fc2))
fib_code = fc2
first_fib_arg = 4
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
int x = fib(%d);
}
""" % first_fib_arg,
line_offset=11,
code_scale=0.6,
)
main_frame = StackFrame(main_code,
'main()',
13, ['x'],
width=2.5,
text_scale=0.6)
main_code.highlight_lines(13)
VGroup(main_code,
main_frame).arrange(RIGHT, buff=LARGE_BUFF * 2).to_edge(DOWN)
tree_area_frame = Polygon(
np.array((-FRAME_X_RADIUS, FRAME_Y_RADIUS, 0)),
np.array((fib_code.get_corner(UL)[0], FRAME_Y_RADIUS, 0)),
np.array((fib_code.get_corner(DL)[0], main_code.get_top()[1], 0)),
np.array((-FRAME_X_RADIUS, main_code.get_top()[1], 0)),
mark_paths_closed=True,
close_new_points=True,
)
ready_desc = TextMobject(
"We'll compute $F_%d$\\\\and track \\textit{all} "
"our work as we go" % first_fib_arg)
ready_desc.move_to(tree_area_frame)
self.play(FadeIn(ready_desc))
self.wait(duration=2)
self.play(
fib_code.to_edge,
UP,
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
tree_text_scale = 1.0
tmp_leaf = TextMobject('$F_%d$' % 1).scale(tree_text_scale)
leaf_width = tmp_leaf.get_width()
level_spread_factors = [4, 1.9, 1.75]
level_spreads = [f * leaf_width for f in level_spread_factors]
tree = BinaryTree(
max_depth=first_fib_arg,
leaf_height=tmp_leaf.get_height(),
level_buff=LARGE_BUFF * 1.5,
level_spreads=level_spreads,
text_scale=tree_text_scale,
)
def update_for_return(current_node, val, run_ctx):
v = TextMobject(str(val))
# v = TextMobject(current_node.label.tex_string, '$=%d$' % val)
v.set_color(GREEN_SCREEN)
v.scale(tree_text_scale)
v.move_to(current_node.label)
self.play(ReplacementTransform(current_node.label, v))
self.wait(duration=run_ctx['update_node_delay'])
extra_anims = []
if current_node.parent:
sr = SurroundingRectangle(current_node.parent)
extra_anims.append(ReplacementTransform(tree.current_rect, sr))
tree.current_rect = sr
extra_anims.append(
ApplyMethod(current_node.parent.set_color, YELLOW))
else:
extra_anims.append(FadeOut(tree.current_rect))
return extra_anims
def call_fib(run_ctx, call_stack, current_node, n):
run_ctx['call_count'] += 1
call_ret_delay = 0.5
stack_frame = StackFrame(fib_code,
'fib(%d)' % n,
1, ['n', 'fn1', 'fn2'],
width=call_stack[0].width,
text_scale=call_stack[0].text_scale)
sr = SurroundingRectangle(current_node)
extra_anims = [current_node.set_color, YELLOW]
if tree.current_rect:
extra_anims.append(ReplacementTransform(tree.current_rect, sr))
else:
extra_anims.append(ShowCreation(sr))
tree.current_rect = sr
if current_node.parent:
extra_anims.append(
ApplyMethod(current_node.parent.set_color, ORANGE))
call_stack.animate_call(stack_frame, self, extra_anims=extra_anims)
self.play(
*stack_frame.get_update_line_anims(2),
stack_frame.update_slot,
'n',
n,
)
if n == 0:
self.play(*stack_frame.get_update_line_anims(3))
self.wait(duration=call_ret_delay)
extra_anims = []
if run_ctx['call_count'] == 5:
s1 = TextMobject("and we know $F_0=0$")
s1.move_to(tree_area_frame).shift(DOWN)
self.play(FadeIn(s1))
extra_anims.append(FadeOut(s1))
extra_anims.extend(update_for_return(current_node, 0, run_ctx))
call_stack.animate_return(self, extra_anims=extra_anims)
return 0
self.play(*stack_frame.get_update_line_anims(5))
if n == 1:
self.play(*stack_frame.get_update_line_anims(6))
self.wait(duration=call_ret_delay)
extra_anims = []
if run_ctx['call_count'] == 4:
s1 = TextMobject("we know $F_1=1$")
s1.move_to(tree_area_frame).shift(DOWN)
self.play(FadeIn(s1))
extra_anims.append(FadeOut(s1))
extra_anims.extend(update_for_return(current_node, 1, run_ctx))
call_stack.animate_return(self, extra_anims=extra_anims)
return 1
self.play(*stack_frame.get_update_line_anims(8))
self.wait(duration=call_ret_delay)
s1 = None
if run_ctx['call_count'] == 1:
s1 = TextMobject('we need $F_3$ and $F_2$')
s1.move_to(tree_area_frame)
self.play(FadeIn(s1))
self.wait()
elif run_ctx['call_count'] == 2:
s1 = TextMobject('and now we need $F_2$ and $F_1$')
s1.move_to(tree_area_frame).shift(DOWN)
self.play(FadeIn(s1))
self.wait()
left_node, ll = tree.add_left_node(current_node,
'$F_%d$' % (n - 1))
right_node, rl = tree.add_right_node(current_node,
'$F_%d$' % (n - 2))
left_node.set_color(BLUE)
right_node.set_color(BLUE)
self.add(ll, rl,
tree.current_rect) # Keep the rect on top of lines
self.play(*[FadeIn(o) for o in [left_node, ll, right_node, rl]])
if s1:
self.wait()
self.play(FadeOut(s1))
s1 = None
fn1 = call_fib(run_ctx, call_stack, left_node, n - 1)
if run_ctx['call_count'] == 4:
s1 = TextMobject("now do the other half")
s1.move_to(tree_area_frame).shift(DOWN)
self.play(FadeIn(s1))
elif run_ctx['call_count'] == 6:
t1 = TextMobject("Using a ``tree'' for this is \\textit{much} "
"more helpful!").scale(0.8)
t2 = TextMobject("Shows where we've ", "been", ", where we ",
"are", ",\\\\and where we're ", "going")
t2.scale(0.8)
t2.set_color_by_tex_to_color_map({
"been": GREEN_SCREEN,
"are": YELLOW,
"going": BLUE,
})
t1.move_to(tree_area_frame).shift(DOWN)
t2.next_to(t1, DOWN, buff=MED_SMALL_BUFF)
self.play(FadeIn(t1))
self.wait()
self.play(Write(t2))
self.wait()
run_ctx['final_desc'] = VGroup(t1, t2)
self.play(
*stack_frame.get_update_line_anims(9),
stack_frame.update_slot,
'fn1',
fn1,
)
if s1:
self.wait()
self.play(FadeOut(s1))
s1 = None
self.wait(duration=call_ret_delay)
fn2 = call_fib(run_ctx, call_stack, right_node, n - 2)
extra_anims = []
if run_ctx['call_count'] == 5:
s1 = TextMobject("add the two halves")
s1.move_to(tree_area_frame).shift(DOWN)
self.play(FadeIn(s1))
extra_anims.append(FadeOut(s1))
run_ctx['update_node_delay'] = 0.1
self.play(
*stack_frame.get_update_line_anims(10),
stack_frame.update_slot,
'fn2',
fn2,
)
self.wait(duration=call_ret_delay)
extra_anims.extend(
update_for_return(current_node, fn1 + fn2, run_ctx))
call_stack.animate_return(self, extra_anims=extra_anims)
return fn1 + fn2
root_node, _ = tree.add_left_node(None, '$F_%d$' % first_fib_arg)
root_node.move_to(tree_area_frame)
root_node.to_edge(UP)
self.play(ShowCreation(root_node))
self.wait()
self.play(FadeOut(ready_desc))
run_ctx = {
'call_count': 0,
'update_node_delay': 1.0,
}
result = call_fib(run_ctx, CallStack(main_frame, scroll_height=1),
root_node, first_fib_arg)
self.play(
*main_frame.get_update_line_anims(14),
main_frame.update_slot,
'x',
result,
)
self.wait(duration=2)
self.play(FadeOutAndShiftDown(main_code),
FadeOutAndShiftDown(main_frame))
self.wait()
t1 = TextMobject("It is common to see recursive algorithms "
"described with trees")
t2 = TextMobject("\\textit{Try drawing them out as you go!}")
t2.set_color(GREEN)
t2.to_edge(DOWN)
t1.next_to(t2, UP, buff=MED_LARGE_BUFF)
self.play(FadeInFromDown(t1))
self.wait(duration=1.5)
self.play(Write(t2))
self.wait(duration=5)
x = self.camera.get_mobjects_to_display(self.mobjects)
end_scale_group = VGroup(*x)
end_fade_group = VGroup()
self.animate_yt_end_screen(end_scale_group,
end_fade_group,
end_scale=0.6,
show_elements=False)
def construct(self):
high_quality = False
# - Foo calls bar passing some args. Bar does something, returns.
code_scale = 0.75
main_code = CodeBlock(
'Java',
r"""
public static
void main(String[] args) {
foo();
}
""",
code_scale=code_scale,
)
foo_code = CodeBlock(
'Java',
r"""
static int foo() {
int n = bar(1, 2);
return n;
}
""",
code_scale=code_scale,
)
bar_code = CodeBlock(
'Java',
r"""
static int bar(int x,
int y) {
int a = x + y;
int b = a * 2;
return b;
}
""",
code_scale=code_scale,
)
fbg = VGroup(foo_code, bar_code)
bar_code.next_to(foo_code, DOWN, aligned_edge=LEFT, buff=LARGE_BUFF)
fbg.to_edge(TOP)
title = TextMobject('We have two Java functions, foo() and bar()')
title.to_edge(UP)
self.play(
ShowCreation(title),
FadeInFromDown(fbg),
)
self.wait(duration=2)
# Let's write down what happens when we run this.
t2 = TextMobject("Let's run them and write down\\\\"
"each variable as we go...")
t2.to_edge(LEFT)
self.play(Write(t2), fbg.to_edge, RIGHT, {'buff': MED_SMALL_BUFF})
self.wait()
t3 = TextMobject('Running foo() and bar() by hand').to_edge(UP)
if high_quality:
self.play(ReplacementTransform(VGroup(title, t2), t3))
else:
self.play(FadeOut(title), FadeOut(t2), FadeIn(t3))
self.remove(title, t2)
title = t3
self.wait()
t4 = TextMobject('First, make a place\\\\to write each variable')
t4.next_to(title, DOWN, buff=LARGE_BUFF).to_edge(LEFT)
self.play(FadeIn(t4))
self.wait()
foo_vars = VGroup(TexMobject('n:', '\\_'))
foo_vars.next_to(foo_code, LEFT, buff=LARGE_BUFF * 2)
bar_vars = VGroup(
TexMobject('x:', '\\_'),
TexMobject('y:', '\\_').shift(DOWN * .75),
TexMobject('a:', '\\_').shift(DOWN * 1.5),
TexMobject('b:', '\\_').shift(DOWN * 2.25),
)
bar_vars.next_to(bar_code, LEFT, aligned_edge=TOP, buff=LARGE_BUFF * 2)
self.play(Write(foo_vars))
self.play(Write(bar_vars))
self.wait()
t5 = TextMobject("Start in foo()...")
t5.move_to(t4, aligned_edge=LEFT)
self.play(FadeOut(t4), FadeIn(t5))
self.wait()
foo_code.move_hidden_highlight(2)
self.play(FadeOut(t5), foo_code.highlight_lines, 2)
self.wait()
foo_n_q = TexMobject('?').move_to(foo_vars[0][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
self.play(Write(foo_n_q))
foo_vars.add(foo_n_q)
self.wait()
xi = foo_code.pre_call(bar_code, (1, 3))
self.play(*foo_code.get_control_transfer_counterclockwise(xi), )
bar_code.post_control_transfer(xi, self)
self.wait()
bar_x = TexMobject('1').move_to(bar_vars[0][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
bar_y = TexMobject('2').move_to(bar_vars[1][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(bar_code.get_code().get_lines(2),
VGroup(bar_x, bar_y).get_right(),
stroke_width=3)
self.play(Write(bar_x), Write(bar_y), ShowCreationThenDestruction(a))
bar_vars_extras = VGroup()
bar_vars_extras.add(bar_x, bar_y)
self.play(bar_code.highlight_lines, 3)
self.wait()
bar_a = TexMobject('3').move_to(bar_vars[2][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(bar_code.get_code().get_lines(3),
bar_a.get_right(),
stroke_width=3)
self.play(Write(bar_a), ShowCreationThenDestruction(a))
bar_vars_extras.add(bar_a)
self.play(bar_code.highlight_lines, 4)
self.wait()
bar_b = TexMobject('6').move_to(bar_vars[3][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(bar_code.get_code().get_lines(4),
bar_b.get_right(),
stroke_width=3)
self.play(Write(bar_b), ShowCreationThenDestruction(a))
bar_vars_extras.add(bar_b)
self.play(bar_code.highlight_lines, 5)
self.wait()
xi = bar_code.pre_return(foo_code, 2)
self.play(*bar_code.get_control_transfer_clockwise(xi), )
foo_code.post_control_transfer(xi, self)
self.wait()
foo_n = TexMobject('6').move_to(foo_vars[0][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(foo_code.get_code().get_lines(2),
foo_n.get_right(),
stroke_width=3)
self.play(
foo_code.highlight_lines,
3,
ReplacementTransform(foo_n_q, foo_n),
ShowCreationThenDestruction(a),
)
foo_vars.add(foo_n)
self.wait()
# - Now give the variables "homes" in each function. Variables like
# homes; they're warm and safe and sized just for them!
print('Give variables homes')
t1 = TextMobject('So how does the\\\\computer do this?').to_edge(LEFT)
self.play(FadeIn(t1), foo_code.remove_highlight)
self.wait(duration=2)
t2 = TextMobject(
'Every variable is stored\\\\someplace in memory').to_edge(LEFT)
new_title = TextMobject('Where are variables stored?').to_edge(UP)
self.play(
FadeOut(t1),
FadeOut(title),
FadeIn(new_title),
FadeIn(t2),
)
title = new_title
self.wait()
em = TextMobject('M')
slot_height = em.get_height() + SMALL_BUFF * 2
slot_width = em.get_width() * 4 + SMALL_BUFF * 2
def build_var_home(name, value):
var_name = TextMobject(name)
slot_box = Rectangle(height=slot_height,
width=slot_width,
stroke_width=1)
var_value = TextMobject(value)
var_value.move_to(slot_box)
var_name.next_to(slot_box, LEFT)
stack_slot = VGroup(slot_box, var_name, var_value)
return stack_slot
foo_homes = build_var_home('n', '6')
foo_homes.move_to(foo_vars, aligned_edge=LEFT)
self.play(ReplacementTransform(foo_vars, foo_homes))
self.wait()
bar_var_vals = [('x', '1'), ('y', '2'), ('a', '3'), ('b', '6')]
bar_homes = VGroup()
bar_homes_shift = 0
for n, v in bar_var_vals:
bar_homes.add(build_var_home(n, v).shift(DOWN * bar_homes_shift))
bar_homes_shift += 0.75
bar_homes.move_to(bar_vars, aligned_edge=LEFT)
t3 = TextMobject("Each variable lives in a\\\\``slot''").to_edge(LEFT)
self.play(
ReplacementTransform(bar_vars, bar_homes),
# FadeOut(bar_vars),
FadeOut(bar_vars_extras),
FadeIn(bar_homes),
)
self.wait()
self.play(
FadeOut(t2),
FadeIn(t3),
)
self.wait()
# - Now arrange the homes into a "stack frame".
print('Build stack frames')
t4 = TextMobject(
"All slots for a function\\\\are put together in a\\\\``frame''")
t4.to_edge(LEFT)
self.play(FadeOut(t3), FadeIn(t4))
frame_width = 2.8
foo_vars = [('n', '6')]
foo_frame = StackFrame(foo_code,
'foo()',
3,
foo_vars,
width=frame_width)
foo_frame.move_to(foo_homes, aligned_edge=LEFT).shift(LEFT * .5)
self.play(ReplacementTransform(foo_homes, foo_frame))
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1,2)',
9,
bar_var_vals,
width=frame_width)
bar_frame.move_to(bar_homes, aligned_edge=LEFT).shift(LEFT * .5)
self.play(ReplacementTransform(bar_homes, bar_frame))
self.wait()
t5 = TextMobject("\\textit{They're happy and warm\\\\together!}")\
.scale(0.75).next_to(t4, DOWN, buff=LARGE_BUFF)
self.play(FadeIn(t5))
self.wait()
# Cool, so where do frames live?
print('Where do frames live')
t6 = TextMobject('So where do frames live?').to_edge(LEFT)
self.play(
FadeOut(t5),
FadeOut(t4),
FadeIn(t6),
)
self.wait()
t7 = TextMobject("On the ``call stack''!").next_to(t6,
DOWN,
buff=LARGE_BUFF)
self.play(FadeIn(t7))
self.wait()
new_title = TextMobject('The Call Stack').to_edge(UP)
t1 = TextMobject('Function calls push a new frame\\\\onto the stack')\
.to_edge(LEFT).shift(UP)
t2 = TextMobject('Returning pops a frame off\\\\the stack').next_to(
t1, DOWN, buff=LARGE_BUFF)
box_count = 8
colors = color_gradient([BLUE, ORANGE], box_count)
little_boxes = VGroup(*[
Rectangle(height=0.25, width=0.75, fill_opacity=1, color=colors[i])
for i in range(box_count)
])
little_boxes.arrange(UP, buff=0.1)
little_boxes.next_to(VGroup(foo_code, bar_code), LEFT, buff=LARGE_BUFF)
self.play(
ReplacementTransform(title, new_title),
FadeOut(t6),
FadeOut(t7),
FadeOut(foo_frame),
FadeOut(bar_frame),
FadeIn(t1),
LaggedStartMap(FadeInFrom,
little_boxes,
lambda m: (m, UP),
lag_ratio=1.0,
run_time=4.0),
)
title = new_title
self.wait()
self.play(
FadeIn(t2),
LaggedStartMap(FadeOutAndShift,
VGroup(*reversed(little_boxes)),
lambda m: (m, UP),
lag_ratio=1.0,
run_time=4.0),
)
self.wait(duration=1)
t3 = TextMobject(
"Let's run again and see\\\\the call stack in action...").to_edge(
LEFT)
t3.shift(UP)
self.play(FadeOut(t1), FadeOut(t2), FadeIn(t3))
self.wait()
print('Run with real call stack')
# Let's also put main() into the picture. Start it off-frame upper right
t4 = TextMobject("... and get main()\\\\into the picture.")\
.next_to(t3, DOWN, buff=LARGE_BUFF)
main_code.next_to(title, DOWN, buff=MED_SMALL_BUFF).to_edge(RIGHT)
main_code.shift(UP * 3 + RIGHT * 3)
g = VGroup(main_code, foo_code, bar_code)
self.play(
g.arrange,
DOWN,
{
'aligned_edge': LEFT,
'buff': MED_SMALL_BUFF
},
g.next_to,
title,
DOWN,
{'buff': MED_SMALL_BUFF},
g.to_edge,
RIGHT,
FadeInFromDown(t4),
)
self.wait(duration=2)
t1 = TextMobject('Start in main()...')
t1.next_to(title, DOWN, buff=LARGE_BUFF).to_edge(LEFT)
frame_width = 3.0
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(main_code,
'main()',
3, [('args', args_ref)],
width=frame_width)
main_frame.next_to(g, LEFT, buff=LARGE_BUFF).to_edge(DOWN)
main_code.move_hidden_highlight(3)
self.play(FadeIn(t1), FadeInFromDown(main_frame),
main_code.highlight_lines, 3, FadeOut(t3), FadeOut(t4))
self.wait()
foo_frame = StackFrame(foo_code, 'foo()', 5, ['n'], width=frame_width)
foo_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
b1 = BraceLabel(foo_frame,
'Calling foo()\\\\pushes a frame',
brace_direction=LEFT,
label_constructor=TextMobject)
xi = main_code.pre_call(foo_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(foo_frame, UP),
FadeInFrom(b1, UP),
FadeOut(t1),
)
foo_code.post_control_transfer(xi, self)
self.wait(duration=2)
self.play(foo_code.highlight_lines, 2, foo_frame.set_line, 6,
FadeOut(b1))
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1, 2)',
10, ['x', 'y', 'a', 'b'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
b1 = BraceLabel(bar_frame,
'Calling bar()\\\\pushes a frame',
brace_direction=LEFT,
label_constructor=TextMobject)
xi = foo_code.pre_call(bar_code, (1, 3))
self.play(
*foo_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(bar_frame, UP),
FadeInFrom(b1, UP),
)
bar_code.post_control_transfer(xi, self)
self.wait()
self.play(bar_frame.update_slot, 'x', 1, bar_frame.update_slot, 'y', 2,
FadeOut(b1))
self.play(bar_code.highlight_lines, 3, bar_frame.set_line, 11)
self.wait()
self.play(bar_frame.update_slot, 'a', 3)
self.play(bar_code.highlight_lines, 4, bar_frame.set_line, 12)
self.wait()
self.play(bar_frame.update_slot, 'b', 6)
self.play(bar_code.highlight_lines, 5, bar_frame.set_line, 13)
b1 = BraceLabel(bar_frame,
"Returning pops\\\\bar's frame",
brace_direction=LEFT,
label_constructor=TextMobject)
self.play(FadeIn(b1))
self.wait(duration=2)
xi = bar_code.pre_return(foo_code, 2)
self.play(
*bar_code.get_control_transfer_clockwise(xi),
Uncreate(bar_frame),
FadeOut(b1),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 3, foo_frame.set_line, 7,
foo_frame.update_slot, 'n', 6)
b1 = BraceLabel(foo_frame,
"Returning pops\\\\foo's frame",
brace_direction=LEFT,
label_constructor=TextMobject)
self.play(FadeIn(b1))
self.wait()
xi = foo_code.pre_return(main_code, 3)
self.play(
*foo_code.get_control_transfer_clockwise(xi),
Uncreate(foo_frame),
FadeOut(b1),
)
main_code.post_control_transfer(xi, self)
self.wait()
self.play(main_code.highlight_lines, 4, main_frame.set_line, 4)
self.wait()
t1 = TextMobject(
'And when main() returns\\\\the program ends').to_edge(LEFT)
self.play(FadeIn(t1))
self.wait()
off_screen_code = CodeBlock('Java', 'off_screen')
off_screen_code.shift(UP * 8) # Offscreen up
self.add(off_screen_code)
xi = main_code.pre_return(off_screen_code, 1)
self.play(
*main_code.get_control_transfer_clockwise(xi),
Uncreate(main_frame),
FadeOut(t1),
)
off_screen_code.post_control_transfer(xi, self)
self.wait()
t1 = TextMobject("Alright, let's do a more complicated one!")
self.play(
FadeInFromDown(t1),
FadeOutAndShift(g, RIGHT),
)
self.wait()