题解 | 挑7

#include <iostream>
#include <string>

using namespace std;

int main() {
    int n;
    cin >> n;
    int res = 0;
    for (int i = 1; i <= n; ++i) {
        if (i % 7 == 0) {
            res++;
            continue;
        } else {
            string str = to_string(i);
            for (auto elem : str) {
                if (elem == '7') {
                    res++;
                    break;
                }
            }
        }
    }
    cout << res << endl;

    return 0;
}