A1069 The Black Hole of Numbers (20 point(s))

数字转数组，数组转数字

1. 原文

原题

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:

f 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

2. AC代码

#include<cstdio>
#include<algorithm>
using namespace std;
bool cmp(int x,int y){
	return x>y;
}
void toarray(int num[],int x)
{
	for (int i = 0; i < 4; ++i)
	{
		num[i]=x%10;
		x=x/10;
	}
}
int tonum(int num[]){
	int x=0;
	for (int i = 0; i < 4; ++i)
	{
		x=x*10+num[i];
	}
	return x;
}
int num[10010]={};
int main()
{
	int n;
	scanf("%d",&n);
	while(true){

	    toarray(num,n);

	    sort(num,num+4,cmp);
	    int a=tonum(num);

	    sort(num,num+4);
	    int b=tonum(num);

	    printf("%04d - %04d = %04d\n",a,b,a-b);
	    if (a-b==0||a-b==6174)
	    {
	    	break;
	    }
	    n=a-b;

	}

	return 0;
}