Find the Shortest All-One Decimal Integer Divisible by K

### Problem Return the length of the smallest positive integer consisting entirely of decimal digit1 that is divisible by k. Return-1 if none exists. The integer itself may exceed64-bit range; only its length is returned. ```cpp class Solution { public: int smallestRepunitDivByK(int k); }; ``` ### Examples **Example 1:** ```text Input: k = 7 Output: 6 Explanation: Lengths1 through6 produce remainders1,4,6,5,2,0 modulo7, so111111 is the first divisible repunit. ``` **Example 2:** ```text Input: k = 5 Output: -1 Explanation: An integer ending in1 cannot be divisible by5. ``` ### Constraints - `1 <= k <= 10^5`. ### Contract considerations The answer is a digit count, not the repunit value or its residue. ```hint Read the boundary condition Appending a decimal1 can be simulated entirely modulo k. ``` ### Boundary reminders The answer is a digit count, not the repunit value or its residue.