蓝桥杯 算法训练 ALGO-139 s01串

 1 import java.util.Scanner;
 2 
 3 public class Main {
 4     static StringBuffer sb = new StringBuffer(); 
 5     public static void main(String[] args) {
 6         Scanner sc = new Scanner(System.in);
 7         int n = sc.nextInt();
 8 
 9         if(n == 0){
10             System.out.println("0");
11         }else{
12             f(n , "0");
13         }
14         System.out.println(sb);
15     }
16 
17     private static void f(int n, String s) {
18         String str="";
19 
20         if( n < 0)
21             return;
22         n--;
23         for(int i = 0 ; i < s.length() ; i++){
24             str = s.substring(i , i+1);
25             if(str.equals("0")){
26                 str = "1";
27             }else if(str.equals("1")){
28                 str = "01";
29             }
30 
31             f( n , str);
32 
33             if(n == 0 ){
34                 sb.append(str);
35             }
36         }
37     }
38 }