[刷题] 1019 数字黑洞 (20分)

思路

• 以字符串接收数据
• sort()：数组排序，倒序排序，重新写比较函数
• s.insert(0, 4 – s.length(), ‘0’)：用来给不足4位的时候前面补0
• do while语句，输入6174时也计算一次

#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');
    do {
        string a = s, b = s;
        sort(a.begin(), a.end(), cmp);
        sort(b.begin(), b.end());
        int result = stoi(a) - stoi(b);
        s = to_string(result);
        s.insert(0, 4 - s.length(), '0');
        cout << a << " - " << b << " = " << s << endl;
    } while (s != "6174" && s != "0000");
    return 0;
}

参考

https://www.liuchuo.net/archives/541