[leetcode] Longest Valid Parentheses @python

时间：2014-10-01 02:49:20 收藏：0 阅读：232

Given a string containing just the characters ‘(‘ and ‘)‘, find the length of the longest valid (well-formed) parentheses substring.

For "(()", the longest valid parentheses substring is "()", which has length = 2.

Another example is ")()())", where the longest valid parentheses substring is "()()", which has length = 4.

class Solution:
    # @param s, a string
    # @return an integer
    def longestValidParentheses(self, s):
        #解题思路：返回括号串中合法括号串的长度。使用栈。这个解法比较巧妙，开辟一个栈，压栈的不是括号，而是未匹配左括号的索引！
        maxLen = 0
        stack = []
        last = -1
        for i in range(len(s)):
            if s[i] == ‘(‘:
                stack.append(i)
            else:
                if stack == []:
                    last = i
                else:
                    stack.pop()
                    if stack == []:
                        maxLen = max(maxLen, i - last)
                    else:
                        maxLen = max(maxLen, i - stack[-1])
        return maxLen