I have tried using hashmaps but still getting the timeout error. Can some one explain why?

PHP brute force:

while (((pow(10,$k)-1)/9) % $n !== 0) {
    $k++;
}

Divide all the repunits until one works.

I have to say that it was a really challenging one. Some suggestions if you feel stuck like me several times trying to solve it.

Try to solved it using Euler's totient funtion: look for the smallest divisor, d, of phi(9n) such that 10^d is equiv to 1 under (mod 9n).

phi, divisors, and 10^d mod 9n, should be implemented as efficient as possible.

I am able to test most of the case in http://stdkmd.com/nrr/repunit/. However, I still can't pass the submissin. Not sure any special case I have miseed.

check my code. Its working awesome https://codeshare.io/P4FZd