LeetCode32. Longest Valid Parentheses——动态规划

一、题目

Given a string containing just the characters ‘(’ and ‘)’, return the length of the longest valid (well-formed) parentheses
substring
.

Example 1:

Input: s = “(()”
Output: 2
Explanation: The longest valid parentheses substring is “()”.
Example 2:

Input: s = “)()())”
Output: 4
Explanation: The longest valid parentheses substring is “()()”.
Example 3:

Input: s = “”
Output: 0

Constraints:

0 <= s.length <= 3 * 104
s[i] is ‘(’, or ‘)’.

二、题解

class Solution {
public:
    int longestValidParentheses(string s) {
        int n = s.size();
        vector<int> dp(n,0);
        int res = 0;
        for(int i = 1;i < n;i++){
            if(s[i] == ')'){
                int p = i - dp[i-1] - 1;
                if(p >= 0 && s[p] == '('){
                    dp[i] = dp[i-1] + 2 + (p - 1 >= 0 ? dp[p-1] : 0);
                }
            }
            res = max(res,dp[i]);
        }
        return res;
    }
};