题解 | #密码截取#

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        String s=sc.nextLine();
        int n=s.length();
        if(n<2) {System.out.println(n);return;}
        
        boolean[][] dp=new boolean[n][n];
        for(int i=0;i<n;i++) dp[i][i]=true;
        
        int j,ans=0;
        for(int L=2;L<=n;L++){
            for(int i=0;i<n+1-L;i++){
                j=L+i-1;
                
                if(s.charAt(i)==s.charAt(j))
                    if(L<=3){
                    dp[i][j]=true;
                    }else dp[i][j]=dp[i+1][j-1]; 
                
                else dp[i][j]=false;
                
                if(dp[i][j]){
                    ans=Math.max(L,ans);
                }
            }
            
        }
        
        System.out.println(ans);
    }
}