题目
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.
解题思路
只有当K是2或5的倍数时，才不会被K整除，其他情况遍历整个数列进行判断，具体证明请见视频
代码
class Solution:
def smallestRepunitDivByK(self, K: int) -> int:
if K % 2 == 0 or K % 5 == 0:
return -1
cur, res = 0, 1
while True:
cur = (10 * cur + 1) % K
if cur == 0:
return res
res += 1
