题解 | 挑7

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

// 计算跟7有关的数字的个数，是7的倍数或者是数字中包含其
static int selectRelative7(int n) {
	int count = 0;

	for (int i = 1; i <= n; i++) {
		if (i % 7 == 0) {
			count++;
		}
		else {
			string s = to_string(i);
			
			if (find(s.begin(), s.end(), '7') != s.end()) {
				count++;
			}
		}

	}

	return count;
}

int main()
{
	int n;

	while (cin >> n) {
		cout << selectRelative7(n) << endl;

	}

	return 0;
}