Smallest Integer Divisible by K

LeetCode Q 1015 - Smallest Integer Divisible by K

Given a positive integer K, you need find the smallest positive integer N such that N is divisible by K, and N only contains the digit 1.
Return the length of N. If there is no such N, return -1.

Example 1: Input: 1 ; Output: 1
Explanation: The smallest answer is N = 1, which has length 1.
Example 2: Input: 2 ; Output: -1
Explanation: There is no such positive integer N divisible by 2.
Example 3: Input: 3 ; Output: 3
Explanation: The smallest answer is N = 111, which has length 3.

Note: 1 <= K <= 10^5

Solution

Code:

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

Note using res = res * 10 + 1; if (res % K == 0) is not correct since res may cause Integer Overflow issue! Also this is not as efficient as the above code.