算法训练 求先序排列

 1 import java.math.BigInteger;
 2 import java.util.Arrays;
 3 import java.util.Scanner;
 4 
 5 
 6 public class Main {
 7     static String a;
 8     static String b;
 9     public static void main(String[] args) {
10         Scanner input = new Scanner(System.in);
11         a = input.next();
12         b = input.next();
13         f(0,a.length()-1,b.length()-1);
14                 
15     }
16     public static void f(int a1,int b1,int b2){
17         if(a1>b1)    return;
18         System.out.print(b.charAt(b2));
19         f(a1,a.indexOf(b.charAt(b2))-1,b2-(b1-a.indexOf(b.charAt(b2)))-1);
20         f(a.indexOf(b.charAt(b2))+1,b1,b2-1);
21         
22         
23 
24     }
25 }