【ACM】- PAT.A1069 & PAT. B1019 The Black Hole of Numbers 【水题】

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题目链接

解题思路：

用到了sprintf()函数，把n 以%d 的格式写到str 字符数组中

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AC程序（C++）

/**********************************
*@ID: 3stone
*@ACM: PAT.A1069 The Black Hole of Numbers
*@Time: 18/8/26
*@IDE: VSCode 2018 + clang++
***********************************/
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

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

int main() {

    int n;
    while(scanf("%d", &n) != EOF) {

        char str[10];
        int result = n;

        while(true) {
            sprintf(str, "%d", result);
            if(strlen(str) < 4){ //不足四位，补齐
                for(int i = strlen(str); i < 4; i++){
                    str[i] = '0';
                }
                str[4] = '\0';
            }

            if(str[0] == str[1] && str[0] == str[2] && str[0] == str[3]) {
                printf("%04d - %04d = 0000\n", n, n);
                break;
            } else {
                sort(str, str + 4);
                int a = (str[0] - '0') * 1000 + (str[1] - '0') * 100 + (str[2] - '0') * 10 + str[3] - '0';
                sort(str, str + 4, cmp);
                int b = (str[0] - '0') * 1000 + (str[1] - '0') * 100 + (str[2] - '0') * 10 + str[3] - '0';
                result = b - a;
                printf("%04d - %04d = %04d\n", b, a, result);
                if(result == 6174) break;
            }
        }

    }//while

    return 0;
}