题解 | #最长的括号子串# O(n)时间，我也不知为啥这么慢

class Solution {
public:
    /**
     * 
     * @param s string字符串 
     * @return int整型
     */
    int longestValidParentheses(string s) {
        // write code here
        int len = s.size();
        vector<int> dp(len,0);
        int res = 0;
        for(int i=1;i<len;i++){
            if(s[i] == ')'){
                int pre = i - dp[i-1] - 1;
                if(pre >= 0 && s[pre] == '('){
                    pre--;
                    int p = 0;
                    if(pre >= 0) p = dp[pre];
                    dp[i] = dp[i-1] + 2 + p,res = max(res,dp[i]);
                }
            }
        }
        
        return res;
    }
};