Pat(A) 1069. The Black Hole of Numbers (20)

原题目：

原题链接：https://www.patest.cn/contests/pat-a-practise/1069

1069. The Black Hole of Numbers (20)

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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, 10000).

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

解题报告

题目是找出所有的数字黑洞。
需要注意的是输出顺序以及本身就是特殊数字的情况。

代码

#include "stdio.h"#include <algorithm>#include <vector>using namespace std;int big(int num){    vector<int> arr;    arr.push_back(num / 1000);    arr.push_back(num / 100 % 10);    arr.push_back(num / 10 % 10);    arr.push_back(num % 10);    sort(arr.begin(),arr.end());    return arr[3] * 1000 + arr[2] * 100 + arr[1] * 10 + arr[0];}int small(int num){    vector<int> arr;    arr.push_back(num / 1000);    arr.push_back(num / 100 % 10);    arr.push_back(num / 10 % 10);    arr.push_back(num % 10);    sort(arr.begin(),arr.end());    return arr[0] * 1000 + arr[1] * 100 + arr[2] * 10 + arr[3];}int main(){    int num = 0;    scanf("%d",&num);    int b = big(num);    int s = small(num);    int newnum = b - s;    if (num == newnum)        printf("%04d - %04d = %04d\n",b,s,newnum);    while(num != newnum){        printf("%04d - %04d = %04d\n",b,s,newnum);        num = newnum;        b = big(num);        s = small(num);        newnum = b - s;    }    //system("pause");}