题目

longest-valid-parentheses

算法

* 栈

O(n)

代码

class Solution {

public:

    int longestValidParentheses(string s) {

        int res = 0, start = 0;

        stack<int> m;

        for (int i = 0; i < s.size(); ++i) {

            if (s[i] == '(') m.push(i);

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

                if (m.empty()) start = i + 1;

                else {

                    m.pop();

                    res = m.empty() ? max(res, i - start + 1) : max(res, i - m.top());

                }

            }

        }

        return res;

    }

};