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
[leetcode] Longest Valid Parentheses @python
原文：http://www.cnblogs.com/asrman/p/4002978.html