1069 The Black Hole of Numbers （20 point(s))

问题描述:

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

唯一需要注意的就是输入数据并不为标准的四位数字，如果采用字符数组的方法需要对数字先进行处理。

#include <bits/stdc++.h>
using namespace std;
char RES[5];
bool cmp(char a, char b) {
	return a > b;
}
bool ves() {
	if (RES[0] == RES[1] && RES[1] == RES[2] && RES[2] == RES[3]) return true;
	return false;
}
bool sixonesevenfour() {
	if (!strcmp(RES, "6174")) return true;
	return false;
}
void setvalue(int res, int rev) {
	int temp = res - rev;
	for (int i = 3, j = 0; i >= 0 ; i--, j++) {
		int m = temp / pow(10, i);
		RES[j] = m + '0';
		temp -= m * pow(10, i);
	}
	RES[4] = '\0';
}
int main(){
	int tmp;
	scanf ("%d", &tmp);
	sprintf(RES, "%04d", tmp);
	if(sixonesevenfour()) {
		cout << "7641 - 1467 = 6174";
		return 0;
	}
	if(ves()) {
		printf("%s - %s = 0000", RES, RES);
		return 0;
	}
	while(!sixonesevenfour()) {
		sort(RES, RES + 4, cmp);
		int res = stoi(RES);
		sort(RES, RES + 4);
		int rev = stoi(RES);
		setvalue(res, rev);
		printf ("%04d - %04d = %s\n", res, rev, RES);
	}
	return 0;
}