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.

参考：http://www.cnblogs.com/easonliu/p/3637429.html

 

C++ 代码实现：

#include<iostream>

#include<string>

#include<stack>

using namespace std;



class Solution

{

public:

    int longestValidParentheses(string s)

    {

        stack<int> st;

        if(s.empty())

            return 0;

        bool a[s.length()];

        size_t i;

        for(i=0; i<s.length(); i++)

        {

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

            {

                //还没有匹配的都设置为false

                a[i]=false;

                st.push(i);

            }

            else if(!st.empty()&&s[i]==')')

            {

                //每次匹配设置两个为true

                a[i]=true;

                a[st.top()]=true;

                st.pop();

            }

            else

                a[i]=false;

        }

        int max=0;

        int count=0;

        for(i=0; i<s.length(); i++)

        {

            if(a[i])

                count++;

            else

                count=0;

            if(count>max)

                max=count;

        }

        return max;

    }

};



int main()

{

    Solution s;

    string str="(()";

    cout<<s.longestValidParentheses(str)<<endl;

}