题解 | #密码截取#

import java.util.Scanner;



// f(i,n) = Max(f(i, n),f(i, n-1), f(i+1, n))  最长密码的递归公式

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static boolean isPs(String ps){
        int l = ps.length();
        for(int i = 0; i < l / 2; i++){
            if(ps.charAt(i) != ps.charAt((l - i  - 1))){
                return false;
            }
        }       
        return true;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
      
        String line = in.nextLine();
        int[][] datas = new int[line.length()][line.length()];
        for(int i = 0; i < line.length() ; i++){
            for(int j = i; j >= 0; j--){
                String ps = line.substring(j,i+1);
                boolean sign = Main.isPs(ps);
                if(sign){
                    datas[i][j] = i - j + 1;
                }else{                    
                    datas[i][j] = Math.max(datas[i - 1][j], datas[i][j + 1]);
                }

            }
        }
        System.out.printf("%d", datas[line.length() - 1][0]);
    }
}