pat 甲级 数字处理 A1069 The Black Hole of Numbers (20分)

 

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

参考柳神： https://www.liuchuo.net/archives/2468

#include<iostream>
#include<algorithm> 
using namespace std;
bool cmp(char a,char b){
	return a>b;
} 
int main(){
	string s;
	cin>>s;
    s.insert(0,4-s.length(),'0');
	while(1){
		string s1=s,s2=s;
		sort(s1.begin(),s1.end(),cmp);
	    sort(s2.begin(),s2.end());
	    int result=stoi(s1)-stoi(s2);
        s=to_string(result);
        s.insert(0,4-s.length(),'0');
        cout<<s1<<" - "<<s2<<" = "<<s<<endl;
	    //printf("%04d - %04d = %04d\n",a,b,result);//超时
        if(s=="6174"||s=="0000") break;
	}
	return 0;
}


//另外的方法：
// #include<cstdio>
// #include<algorithm>
// using namespace std;
// void to_array(int a,int num[])
// {
// 	for(int i=0;i<4;i++)
// 	{
// 		num[i]=(a%10);
// 		a=a/10;
// 	}
// }
// int to_number(int num[])
// {
// 	int sum=0;
// 	for(int i=0;i<4;i++)
// 	sum=sum*10+num[i];
// 	return sum;
// }
// bool cmp(int a,int b)
// {
// 	return a>b;
// }
// int main()
// {
// 	int n,num[5],max,min;
// 	scanf("%d",&n);
// 	while(1)
// 	{
// 		to_array(n,num);
// 		sort(num,num+4);
// 		min=to_number(num);
// 		sort(num,num+4,cmp);
// 		max=to_number(num);
// 		n=max-min;
// 		printf("%04d - %04d = %04d\n",max,min,n);
// 		if(n==0||n==6174) break;
// 	}
// 	return 0;
// }