题解 | #挑7#

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

int main() {
    int n;
    cin >> n;
    int t = 1;
    int cur = 0;
    int weight[5] = {1, 10, 100, 1000, 10000};
    while (t <= n) {
        if(t % 7 == 0) {
            cur++;
            t++;
            continue;
        }
        for(int i = 0; i < 5; i++) {
            if((t / weight[i]) % 10 == 7) {
                cur++;
                break;
            }
        }
        t++;
    }
    cout << cur << endl;
}