def is_valid(string: str) -> bool:
"""
Premise for this operation is that if the opening bracket matches the closing bracket next to it, remove from the stack
If the stack isn't empty after iterating through the whole process, it's invalid.
:type string: str
:rtype: bool
"""
stack = Stack()
opens = ['{', '[', '(']
closes = ['}', ']', ')']
matches = {'[': ']', '{': '}', '(': ')'}
if len(string) == 0:
return False
for bracket in string:
if bracket in opens:
stack.push(bracket)
if bracket in closes:
x = stack.top()
y = matches[stack.top()]
if bracket == matches[stack.top()]:
stack.pop()
else:
# i.e. ( ] is invalid always
return False
if stack.length() == 0:
return True
else:
return False
from structs import Stack stack = Stack() stack.push(12) stack.push(13) print(stack.pop()) print(stack.peek()) print(stack.top) print(stack.peek()) print(stack.isEmpty())
