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1015. Smallest Integer Divisible by K

Difficulty Topics

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

smallest-integer-divisible-by-k.py
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