题解 | 挑7

#include <iostream>
#include <string>
using namespace std;

int main() {
    int n;
    cin >> n;

    int counter = 0;
    for (int i = 1; i <= n; i ++) {
        if (i % 7 == 0) {
            counter ++;
        } else {
            string num = to_string(i);
            if (num.find('7') != num.npos) {
                counter ++;
            }
        }
    }

    cout << counter << endl;
    return 0;
}
// 64 位输出请用 printf("%lld")