Description:
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
//NKW 乙级真题1009
#pragma warning(disable:4996)
#include <stdio.h>
#include <stdlib.h>
#include <algorithm>
using namespace std;
bool cmp(int a, int b){
return a > b;
}
int toint(int a[]){
int sum = 0;
for (int i = 0; i < 4; i++)
sum = sum * 10 + a[i];
return sum;
}
void toarray(int a[], int b){
for (int i = 3; i >= 0; i--){
a[i] = b % 10;
b /= 10;
}
}
int main(){
int n, max, min, arr[4];
scanf("%d", &n);
do{
toarray(arr, n);
sort(arr, arr + 4);
min = toint(arr);
sort(arr, arr + 4, cmp);
max = toint(arr);
n = max - min;
printf("%04d - %04d = %04d\n", max, min, n);
} while (n != 0 && n != 6174);
system("pause");
return 0;
}