def parse(self, exp: str) -> None:
stack = Stack()
tokens = math_exp_parser.tokenize_cumulatively(exp)
current_tree: ExpParseTree = self
stack.push(self)
for t in tokens:
if t == "(": # insert a child to the left and move there
current_tree.insert_left(t)
stack.push(current_tree)
current_tree = current_tree.left
elif t == ")": # move up to parent
current_tree = stack.pop()
elif t in [
"+",
"-",
"*",
"/",
]: # set the operator for root, insert a child to the right and move there
current_tree.key = t
new_node = current_tree.insert_right(t)
stack.push(current_tree)
current_tree = current_tree.right
else: # set the value to the current tree's root and move up to parent
current_tree.key = t
current_tree = stack.pop()
def test_push_pop():
s = Stack()
s.push(6)
assert s.pop() == 6
s.push(9)
s.push(15)
assert s.pop() == 15
assert s.pop() == 9
def reverse_str(input: str) -> str:
"""Reverses a string using a Stack data structure.
Arguments:
input {str} -- string to reverse
Returns:
str -- reversed string
"""
stack = Stack()
for c in input:
stack.push(c)
return "".join([stack.pop() for c in range(len(stack))])
def balanced_parantheses(input: str) -> bool:
"""Checks if a given string has balanced opening and closing parantheses, i.e "(" and ")"
Arguments:
input {str} -- Input string to check
Returns:
bool -- True if balanced, False otherwise
"""
stack = Stack()
if len(input) == 0:
return True
for c in input:
if c == "(":
stack.push(c)
elif c == ")":
# the stack shouldn't be empty when we see a closing parantheses
if stack.is_empty():
return False
stack.pop()
return stack.is_empty()
def test_pop_empty_raiseserror():
s = Stack()
with pytest.raises(Exception) as e:
assert s.pop()
assert str(e.value) == Stack.EMPTY_STACK_ERR_MSG
def test_peek():
s = Stack()
s.push("jim jarmusch")
s.push("mike leigh")
s.push("tony gatlif")
assert s.peek() == "tony gatlif"
s.pop()
assert s.peek() == "mike leigh"
s.push("zeki demirkubuz")
assert s.peek() == "zeki demirkubuz"
def test_len():
s = Stack()
s.push(6)
s.pop()
assert len(s) == 0
s.push(9)
s.push(15)
s.pop()
assert len(s) == 1
s.push(21)
assert len(s) == 2