【leetcode】32. 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.
 */
#include <iostream>
#include <string>
#include <stack>
#include <algorithm>
using namespace std;

//找到最长的括号匹配的子串
int longestValidParentheses(string s) 
{
    if (s.empty()) return 0;

    stack<int> st;
    int maxlen = 0;
    for (int i = 0; i < s.length(); i++)
    {
        if (!st.empty() && s[i] == ')' && s[st.top()] == '(')
        {
            st.pop();
            maxlen = max(maxlen, i - st.top());
        }
        else
        {
            st.push(i);
        }
    }

    return maxlen;
}

int main()
{

    string s = "(()";
    cout << longestValidParentheses(s) << endl;

    system("pause");
    return 0;
}