leetcode 20. Valid Parentheses

在学习数据结构中看到栈，因此回想起之前做leetcode时遇到的一题：

Given a string containing just the characters

'('

,

')'

,

'{'

,

'}'

,

'['

and

']'

, determine if the input string is valid.

The brackets must close in the correct order,

"()"

and

"()[]{}"

are all valid but

"(]"

and

"([)]"

are not.

class Solution(object):
def isValid(self, s):
mystack = []
for item in s:
if item in ["(","[","{"]:
mystack.append(item)

if item in [")","]","}"]:
if mystack == []:
return False
top = mystack[-1]
if (top == '(' and item == ')') or (top == "[" and item == "]") or (top == "{" and item == "}"):
mystack.pop()
else:
return False
return len(mystack) == 0