def walk(root, stack):
# record holders for heaviest leaf, and corresponding weight
nonlocal heaviest_leaf
nonlocal heaviest_weight
if not stack:
stack = Stack()
if root.left:
left = self.walk(root.left, stack)
if root.right:
right = self.walk(root.right, stack)
# are we at a leaf node (a node with no children)?
if not root.left and not root.right:
# if we've not encountered any leaf yet, or our current leaf
# is the new heaviest leaf, lets set our record holders
if heaviest_weight is None or (root.value + left + right >
heaviest_weight):
heaviest_leaf = root
heaviest_weight = root.value + left + right
stack.push(root)
else:
stack.pop()
def test_pop():
stack = Stack()
stack.push('Dwight')
stack.push('Michael')
stack.push('Jim')
stack.pop()
actual = stack.top.value
expected = 'Michael'
assert actual == expected
def test_pop_some():
s = Stack()
s.push("apple")
s.push("banana")
s.push("cucumber")
s.pop()
actual = s.pop()
expected = "banana"
assert actual == expected
def test_pop_until_empty():
s = Stack()
s.push("apple")
s.push("banana")
s.push("cucumber")
s.pop()
s.pop()
s.pop()
actual = s.is_empty()
expected = True
assert actual == expected
def test_pop_till_empty():
stack = Stack()
stack.push('Dwight')
stack.push('Michael')
stack.push('Jim')
stack.pop()
stack.pop()
stack.pop()
actual = stack.is_empty()
expected = True
assert actual == expected
def validate_string(string):
stack = Stack()
# opening symbols
opening = '{[('
# closing symbols, must be in the matched order of opening
closing = '}])'
# iterate through the string we are testing
for char in string:
# if we encounter an opening symbol, push it to the stack
if char in opening:
stack.push(char)
# if we encounter a closing symbol, check if it matches the top of the stack
elif char in closing:
i = closing.index(char)
if stack.is_empty() or stack.pop() != opening[i]:
return False
# if we've not matched all the symbols... fail!
if not stack.is_empty:
return False
# we have matched all the symbols, success!
return True
class PseudoQueue():
def __init__(self):
self.input = Stack()
self.output = Stack()
def enqueue(self, value):
self.input.push(value)
def dequeue(self):
# Empty the input stack into output stack
if self.input:
try:
value = self.input.pop()
self.output.push(value)
except Exception:
return("Unable to successfully dequeue")
# Return top of the output stack
return self.output.pop()
class PseudoQueue:
"""Creates instance of Queue using stacks to track front and rear of queue
"""
def __init__(self) -> object:
"""PseudoQueue instance. front and back are represented by stack objects
"""
self.front = Stack()
self.rear = Stack()
def __str__(self) -> str:
"""String Literal showing PseudoQueue instance current front and back
"""
return f'A PseudoQueue instance current front value: {self.front.peek()}current rear value: {self.rear.peek()}'
def enqueue(self, value):
"""Adds a node to the PseudoQueue instance
input <-- any
output --> non-fruitful (mutates instance of PseudoQueue in place)
"""
if not self.front.top:
self.front.push(value)
self.rear.top = self.front.top
else:
curr_rear = self.rear.top
self.rear.push(value)
curr_rear.next = self.rear.top
def dequeue(self):
if self.front.top.next == None:
raise InvalidOperationError(
'Method not allowed on an empty collection')
else:
new_front = self.front.top.next
temp = self.front.pop()
self.front.push(new_front.value)
return temp
class PsuedoQueue:
"""
This is a queue being implement using stack's
push, pop and peek methods rather than having
its own attributes and methods
"""
def __init__(self):
self.front_stack = Stack()
self.rear_stack = Stack()
# this is strictly here so that we may pass a test,
self.front = None
def peek(self):
return self.front_stack.peek()
def is_empty(self):
return self.front_stack.is_empty()
def enqueue(self, value=None):
node = Node(value)
if self.rear_stack.top:
self.rear_stack.top.next = node
self.rear_stack.top = node
if not self.front_stack.top:
self.front_stack.top = node
# next line is solely here to pass a test
self.front = self.front_stack.top
def dequeue(self):
# if the queue only holds one node, we must manually set the rear to None
if (self.rear_stack.top == self.front_stack.top):
self.rear_stack.top = None
value = self.front_stack.pop()
# next line is solely here to pass a test
self.front = self.front_stack.top
return value
def test_pop_empty():
s = Stack()
with pytest.raises(InvalidOperationError) as e:
s.pop()
assert str(e.value) == "Method not allowed on empty collection"
def test_pop():
s = Stack()
s.push("apple")
actual = s.pop()
expected = "apple"
assert actual == expected