Description
Given a positive integer k, you need to find the length of 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.
Note: n may not fit in a 64-bit signed integer.
Example 1:
Input: k = 1 Output: 1 Explanation: The smallest answer is n = 1, which has length 1.
Example 2:
Input: k = 2 Output: -1 Explanation: There is no such positive integer n divisible by 2.
Example 3:
Input: k = 3 Output: 3 Explanation: The smallest answer is n = 111, which has length 3.
Constraints:
1 <= k <= 105
Solution
Python3
class Solution:
def smallestRepunitDivByK(self, k: int) -> int:
if k % 2 == 0 and k % 5 == 0: return -1
mod_set = set()
prev = 0
for i in range(1, k + 1):
prev = (prev * 10 + 1) % k
if prev == 0: return i
if prev in mod_set: return -1
mod_set.add(prev)
return -1