【PAT甲級 前導0，排序】1069 The Black Hole of Numbers (20 分) C++ 全部AC

題目

一直循環相減即可，直到結果爲6174或者四個數字相同就結束循環

---

題解 C++

#include<iostream>
#include<stdio.h>
#include<algorithm>
using namespace std;
int cmp1(int a, int b) {
	return a > b;
}
int cmp2(int a, int b) {
	return a < b;
}
int main() {
	int num;
	cin >> num;


	//循環計算
	int cha;
	do {
		//分離四位
		int saveNum = num;
		int arr[4];
		for (int i = 0; i < 4; i++) {
			arr[i] = num % 10;
			num /= 10;
		}

		//是否四位都相同
		if (arr[0] == arr[1] && arr[1] == arr[2] && arr[2] == arr[3]) {
			printf("%04d - %04d = %04d", saveNum, saveNum, 0);
			system("pause");
			return 0;
		}

		//大到小
		sort(arr, arr + 4, cmp1);
		int big = arr[0] * 1000 + arr[1] * 100 + arr[2] * 10 + arr[3];

		//小到大
		sort(arr, arr + 4, cmp2);
		int small = arr[0] * 1000 + arr[1] * 100 + arr[2] * 10 + arr[3];

		cha = big - small;

		printf("%04d - %04d = %04d\n", big, small, cha);

		num = cha;
	} while (cha != 6174);

	system("pause");
}