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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{ public: int longestValidParentheses(string s){ stack<int> lefts; // index of left parentheses. int len = s.length(); if(len < 2) return 0; int start = -1; int res = 0; for (int i=0;i<len;i++){ if(s[i] == ‘(‘){ lefts.push(i); }else{ if(lefts.empty()){ start = i; }else{ lefts.pop(); if(lefts.empty()){ res = max(res,i - start); }else{ res = max(res,i- lefts.top()); } } } } return res; } };
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原文地址：http://www.cnblogs.com/wxquare/p/5928842.html
