2016腾讯笔试 最大回文串 变种

/**
 * 求一个字符串的最大回文串，可以在两边和中间删除任意多个字符，使剩下的字符串为回文串
 * 可以使用回溯法
 */
import java.util.Scanner;

public class Palindrome {
    static int[] flag;
    static int length;
    static String s;
    static int maxLength;
    static String maxString;
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            s = sc.next();
            length = s.length();
            flag = new int[length];
            maxLength = 0;
            f(0);
            System.out.println(maxString + " " + maxLength);
        }
    }
    
    public static void f(int n){
        //递归出口
        if(n==length){
            StringBuffer sb = new StringBuffer();
            for(int i=0;i<length;i++){
                if(flag[i]==1){
                    sb.append(s.charAt(i));
                }
            }
            //判断回文串
            if(sb.toString().equals(sb.reverse().toString())&&sb.length()>maxLength){
                maxString = sb.toString();
                maxLength = sb.length();
            }
            return;
        }
        
        //要
        flag[n]=1;
        f(n+1);
        
        //不要
        flag[n]=0;
        f(n+1);
    }
}