题解 | #挑7#

解题思路：

1、能够被7整除，则一定是7的倍数
2、不能被7整除，判断是否包含数字7

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int count = 0;
        for (int i = 7; i <= n; i++) {
            if (isContains(i)) {
                count++;
            }
        }
        System.out.println(count);
    }
    public static boolean isContains(int num) {
        String val = String.valueOf(num);
        return val.indexOf("7") != -1 || num % 7 == 0;
    }
}