题目描述:(链接）
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.
题目解析：
用栈！
1 class Solution { 2 public: 3 int longestValidParentheses(string s) { 4 vector<int> cache; 5 int last = -1; //最后一个‘）‘ 6 int max_len = 0; 7 for (int i = 0; i < s.size(); ++i) { 8 if (s[i] == ‘)‘) { 9 if (cache.empty()) { 10 last = i; 11 } else { 12 cache.pop_back(); 13 if (cache.empty()) { 14 max_len = max(max_len, i - last); 15 } else { 16 max_len = max(max_len, i - cache.back()); 17 } 18 } 19 } else { 20 cache.push_back(i); 21 } 22 } 23 return max_len; 24 } 25 };
[LeetCode]Longest Valid Parentheses
原文：http://www.cnblogs.com/skycore/p/4972428.html