def parentheses(str):
s = stack.Stack()
item = {'{': '}', '(': ')'}
for i in range(len(str) - 1):
if str[i] == '{' or str[i] == '(':
s.push(str[i])
if s.peek() is None:
return False
if item[s.peek()] == str[i + 1]:
s.pop()
return s.size == 0
def is_palindrome(str):
s = stack.Stack()
half = int(len(str) / 2)
for i in range(half):
s.push(str[i])
if len(str) % 2 == 1:
half += 1
while s.size != 0:
if s.pop() == str[half]:
half += 1
else:
return False
return True
def reverse_stack(item):
tmp = copy.deepcopy(item)
reverse = stack.Stack()
for i in range(tmp.size):
reverse.push(tmp.pop())
return reverse
