【编程题】数字黑洞

　　附上Java实现代码。

 1 package NetEasy;
 2
 3 /**
 4  * 数字黑洞
 5  */
 6
 7 import java.util.Scanner;
 8
 9 public class NumBlackHole {
10
11     public static void main(String[] args) {
12         Scanner in = new Scanner(System.in);
13         String number = in.next();
14 //        StringBuffer numStr = new StringBuffer();
15 //        numStr.append(number);
16         if(number.charAt(0)==number.charAt(1) &&
17                 number.charAt(0)==number.charAt(2)&&
18                 number.charAt(0)==number.charAt(3))
19             System.out.println(number+" - "+number+" = 0");
20         else{
21             boolean flag = true;
22 //            int num = Integer.valueOf(number);
23             while(flag){
24                 number = computeNum(number);
25                 if(number.equals("6174"))
26                     flag = false;
27             }
28         }
29
30     }
31
32     private static String computeNum(String number) {
33 //        String number = Integer.valueOf(num).toString();
34         StringBuffer numOrder = new StringBuffer(number);
35         for(int i = 0; i < 4; i++){
36             for(int j = i; j < 4; j++){
37                 if(numOrder.charAt(i) < numOrder.charAt(j)){
38                     char temp = numOrder.charAt(i);
39                     numOrder.setCharAt(i, number.charAt(j));
40                     numOrder.setCharAt(j, temp);
41                 }
42             }
43         }
44 //        StringBuffer numUpper = numOrder;  //这样复制，后面numOrder反转了 numUpper会跟着变化
45         String numUpper = numOrder.toString();
46         String numLower = numOrder.reverse().toString();
47         int n = Integer.valueOf(numUpper)-Integer.valueOf(numLower);
48         StringBuffer result = new StringBuffer(Integer.valueOf(n).toString());
49         if(result.length() == 1)
50             result.insert(0, "000");
51         if(result.length() == 2)
52             result.insert(0, "00");
53         if(result.length() == 3)
54             result.insert(0, "0");
55         String resultnum = result.toString();
56         System.out.println(numUpper+" - "+numLower+" = "+ resultnum);
57         return resultnum;
58     }
59
60 }