题解 | 密码截取

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.nextLine();
        int[][] dp = new int[s.length()][s.length()];
        for (int i = 0; i <= s.length() - 1; i++) {
            dp[i][i] = 1;
        }
        for (int i = 0; i <= s.length() - 2; i++) {
            if (s.charAt(i) == s.charAt(i + 1)) {
                dp[i][i + 1] = 2;
            } else {
                dp[i][i + 1] = 0;
            }

        }
        for (int j = 3; j <= s.length(); j++) {
            for (int i = 0; i <= s.length() - j; i++) {
                int end = i + j - 1;
                if (s.charAt(i) == s.charAt(end) && dp[i + 1][end - 1] > 0) {
                    dp[i][end] = dp[i + 1][end - 1] + 2;
                } else {
                    dp[i][end] = 0;
                }
            }
        }
        int maxLen = 1;
        for (int i = 0; i < s.length(); i++) {
            for (int k = i; k < s.length(); k++) {
                if (dp[i][k] > maxLen) {
                    maxLen = dp[i][k];
                }
            }
        }
        System.out.println(maxLen); // 仅打印最终长度

        in.close();
    }
}