PAT 1069 The Black Hole of Numbers[简单]

1069 The Black Hole of Numbers（20 分）

For any 4-digit integer except the ones with all the digits being the same, if we sort the digits in non-increasing order first, and then in non-decreasing order, a new number can be obtained by taking the second number from the first one. Repeat in this manner we will soon end up at the number 6174 -- the black hole of 4-digit numbers. This number is named Kaprekar Constant.

For example, start from 6767, we'll get:

7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174
7641 - 1467 = 6174
... ...

Given any 4-digit number, you are supposed to illustrate the way it gets into the black hole.

Input Specification:

Each input file contains one test case which gives a positive integer N in the range (0,10​4​​).

Output Specification:

If all the 4 digits of N are the same, print in one line the equation N - N = 0000. Else print each step of calculation in a line until 6174 comes out as the difference. All the numbers must be printed as 4-digit numbers.

Sample Input 1:

6767

Sample Output 1:

7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174

Sample Input 2:

2222

Sample Output 2:

2222 - 2222 = 0000

 题目大意：给定一个四位数，展示出每位数从大到小排列，与从小到大排列的差值，直到出现6174黑洞数停止。

//这道题目是简单的，但是还是遇见了一些问题：

AC：

#include <iostream>
#include <algorithm>
#include <vector>
#include <stdlib.h>
#include<cstdio>
using namespace std;

int main()
{
    int n;
    cin>>n;
    int a[4],big,small,res=-1;
    int temp=0;
    while(res!=6174)
    {
        fill(a,a+4,0);
        while(n!=0)
        {
            a[temp++]=n%10;
            n/=10;
            //cout<<"kk";
        }
        temp=0;
        sort(a,a+4);//默认从小到大排列
        small=a[0]*1000+a[1]*100+a[2]*10+a[3];
        big=a[3]*1000+a[2]*100+a[1]*10+a[0];
        if(a[0]==a[1]&&a[1]==a[2]&&a[2]==a[3])
        {
            printf("%04d - %04d = 0000
",big,small);
            return 0;
        }
        res=big-small;
        printf("%04d - %04d = %04d
",big,small,res);
        n=res;
    }
    return 0;
}

1.第一次忽略了temp=0；应该在使用过后将其赋值为0的；

2. 应该将a数组初始化为0，要不然下次会有影响的，比如在有0位的时候：

3.最后就是提交发现第0个测试点过不去，原来是因为相同数的时候只输出了0，而不是0000！