最长有效括号

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