算法-子串子序列最值问题

leetcode 32.最长有效括号

左神 中级提升班 3-2

class Solution {
    public int f(String s) {
        //1
        char[] chs = s.toCharArray();
        int n = s.length();
        //表示以i结尾的最长有效子串
        int[] dp = new int[n];
        dp[0] = 0;
        //2
        for (int i = 1; i < n; i++) {
            //analyse chs[i]
            if (chs[i] == '(') {
                dp[i] = 0;
            } else {
                if (i - dp[i - 1] - 1 >= 0 && chs[i - dp[i - 1] - 1] == '(') {
                    dp[i] = dp[i - 1] + ((i - dp[i - 1] - 2 >= 0) ? dp[i - dp[i - 1] - 2] : 0) + 2;
                }
            }
        }
        int ans = -1;
        for (int i = 0; i < n; i++) {
            ans = Math.max(ans, dp[i]);
        }
        return ans;
    }
}