def is_balanced(parens: str):
"""Checks to see if a string of parens are balanced"""
stack = Stack()
try:
for paren in parens:
if stack.is_empty() or (not stack.is_empty() and paren == stack.peek()):
stack.push(paren)
else:
stack.pop()
return stack.is_empty()
except IndexError:
return False
class MyQueue:
def __init__(self):
self.stack1 = Stack(0)
self.stack2 = Stack(0)
self.stack1.pop()
self.stack2.pop()
self.use1 = True
def add(self, value):
if self.use1:
self.stack1.push(value)
else:
self.stack2.push(value)
def remove(self):
if self.use1:
self.use1 = not self.use1
while (not self.stack1.isEmpty()):
self.stack2.push(self.stack1.pop())
return self.stack2.pop()
else:
self.use1 = not self.use1
while (not self.stack2.isEmpty()):
self.stack1.push(self.stack2.pop())
return self.stack1.pop()
def postfixeval(list):
values = Stack()
for token in list:
if token in "0123456789":
values.push(int(token))
else:
if token in "()":
continue
else:
op1 = values.pop()
op2 = values.pop()
result = calculate(token,op1,op2)
values.push(result)
return values.pop()
print values
def reverse_level_order(self):
to_traverse = [self.root]
stack = Stack(100)
while len(to_traverse) > 0:
node = to_traverse[0]
data = node.value
stack.push(Node(data))
if node.right:
to_traverse.append(node.right)
if node.left:
to_traverse.append(node.left)
to_traverse.pop(0)
traversal = []
for x in range(stack.size):
traversal.append(stack.pop().get_value())
return traversal
def dfsPrint(self, start):
if start is None:
return
stack = Stack()
stack.push(start)
traversal = ""
while len(stack) > 0:
traversal += str(stack.peek().value) + "->"
node = stack.pop()
if node.left:
stack.push(node.left)
if node.right:
stack.push(node.right)
return traversal
def dfsSize(self):
if self.root is None:
return 0
stack = Stack()
head = self.root
if head is not None:
stack.push(head)
count = 0
while len(stack) > 0:
count += 1
node = stack.pop()
if node.left is not None:
stack.push(node.left)
if node.right is not None:
stack.push(node.right)
return count
def parChecker(string):
s=Stack()
balanced=True
index=0
while index<len(string) and balanced:
symbol=string[index]
if symbol in "([{":
s.push(symbol)
else:
if s.isEmpty():
balanced=False
else:
top=s.pop()
## we have to see the top that we have removed matches the symbol
if not matches(top,symbol):
balanced=False
index+=1
if balanced and s.isEmpty():
return True
else:
return False
def reverse_levelorder_print(self, start):
if start is None:
return
queue = Queue()
stack = Stack()
queue.enqueue(start)
traversal = ""
while len(queue) > 0:
node = queue.dequeue()
stack.push(node)
if node.right:
queue.enqueue(node.right)
if node.left:
queue.enqueue(node.left)
while len(stack) > 0:
node = stack.pop()
traversal += str(node.value) + "-"
return traversal
class Stack(object):
def __init__(self):
self.ll = LinkedList()
def isEmpty(self):
return self.ll.isEmpty()
def push(self, data):
self.ll.addNode(Node(data))
def pop(self):
self.ll.delEnd()
def peek(self):
return self.ll.returnEndElement()
def size(self):
return self.ll.size()
s = Stack()
s.push(133)
s.push(24)
s.push(123)
s.push(12124)
s.pop()
print s.peek()
print s.size()