leetcode Longest Valid Parentheses

题目连接

https://leetcode.com/problems/longest-valid-parentheses/ 

Longest Valid Parentheses

Description

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. 

记录括号出现的位置，找连续最长的一段。。

class Solution {
public:
	int longestValidParentheses(string s) {
		if (s.empty()) return 0;
		int n = s.length();
		stack<int> st;
		vector<bool> vis(n + 10);
		for (int i = 0; i < n; i++) {
			char &c = s[i];
			if (c == '(') {
				st.push(i);
			} else if (c == ')' && !st.empty()){
				vis[i] = true;
				vis[st.top()] = true; st.pop();
			}
		}
		int ans = 0, ret = 0;
		for (int i = 0; i < n; i++) {
			if (vis[i]) ++ret;
			else ret = 0;
			ans = max(ans, ret);
		}
		return ans;
	}
};