Leetcode 栈 Valid Parentheses

Valid Parentheses

Total Accepted: 17916 Total
Submissions: 63131My Submissions

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.

题意：有三对括号‘(‘和‘)‘，‘[‘和‘]‘，‘{‘和‘}‘，判断给定的括号字符串是否匹配

思路：用栈

1.遇到左括号就压栈

2.遇到右括号就判断栈顶的括号和当前的括号是否是一对，如果栈为空或不匹配，说明整个字符串的括号不匹配，如果匹配，则将栈顶括号出栈

3.如果最终栈中的元素为0，则说明字符串匹配，否则不匹配

复杂度：时间O(n)，空间O(n)

class Solution:

# @return a boolean

def isValid(self, s):

if s == ‘‘: return True

stack = []

left = ‘([{‘;right = ‘)]}‘

for c in s:

if c == ‘(‘ or c == ‘[‘ or c ==‘{‘:

stack.append(c); continue

for i in xrange(3):

if c == right[i]:

if not stack or stack[-1] != left[i]:

return False

else:

stack.pop(); continue

return not stack