技術標籤：演算法筆記c++

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.

1. 頻繁使用的轉換可封裝成函式
2. 輸出格式非常重要

#include <stdio.h>
#include <algorithm>
 

#include <math.h>

using namespace std;

void num_to_array(int n,int a[]){
    for(int i=0;i<4;i++){
            a[i]=n%10;
            n/=10;
        }
}

int array_to_num(int a[]){
    int n=0;
    for(int i=0;i<4;i++){
            n=n*10+a[i];
        }
    return n;
}

bool cmp(int a,int b)
 
{
    return a>b;
}

int main(){
    int n,a[4];
    scanf("%d",&n);
    num_to_array(n,a);
    do{
        int n1,n2;
        sort(a,a+4);
        n1=array_to_num(a);
        sort(a,a+4,cmp);
        n2=array_to_num(a);
        n=n2-n1;
        printf("%04d - %04d = %04d\n",n2,n1,n);
        /*%d左對齊，輸出變數的所有數字；
        %4d右對齊，寬度為4，左邊填充空格，當變數的實際寬度大於4時，輸出變數的所有數字；
        %04d與%4d的唯一區別就是左邊填充0。*/
        num_to_array(n,a);
    }while(n!=6174&&n!=0);
    return 0;
}