https://leetcode.com/problems/smallest-integer-divisible-by-k/

smallest-integer-divisible-by-k.java

class Solution {
    public int smallestRepunitDivByK(int K) {
        if (K == 2 || K == 5) {
            return -1;
        }
        int num = 0;
        
        for (int i = 1; i <= K; i++) {
            num = (num * 10 + 1) % K;
            if (num == 0) {
                return i;
            }
        }
        return -1;
    }
}