题解 | 最长回文子序列

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 int longest(String s) {
        int n = s.length();
        int [][]dp = new int [n][n];
        for (int i = 0; i < n; i++) {
            dp[i][i] = 1;
        }
        for (int length = 2; length <= n; length++) {
            for (int i = 0; i <= n - length; i++) {
                int j = i + length - 1;
                if (s.charAt(i) == s.charAt(j)) {
                    if (length == 2) {
                        dp[i][j] = 2;
                    } else {
                        dp[i][j] = dp[i + 1][j - 1] + 2;
                    }
                } else {
                    dp[i][j] = Math.max(dp[i + 1][j], dp[i][j - 1]);
                }
            }
        }
        return dp[0][n - 1];
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine().trim();
        scanner.close();
        System.out.println(longest(input));
    }
}