LeetCode_Longest Valid Parentheses

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.

　　用一个stack来维护上一个未匹配的位置，当出现匹配情况时更新最大值

class Solution {

public:

    int longestValidParentheses(string s) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

     

        int n = s.length();

        if(n < 2) return 0;

        

        int maxR = 0 , top,result ;

        stack<int> myS;

        

        for(int i = 0; i < n; i++)

        {

          if(s[i] == '(' || myS.empty())

                myS.push(i);

                

          else 

          {

             top = myS.top();

             if(s[top] == '(')                

             {

                myS.pop();  

                result = myS.empty()? i+1: i - myS.top();

                maxR = maxR > result ? maxR : result ;

            }else   

                myS.push(i);  

             

          }

        }

        

        return maxR;

    }

};