I'm laughing now ....
I've spent about 3 hours for this problem.
First off, I used Z-function and I tried to treat problem as a string problem. I generated new string and tried to find it. If there is no, that's the answer.
It became not so slow as can seems to be. But TLE#6 got me!
Then I tried to store positions for each digit(0-9) and than tried to search target number using binary search for every digit. It works, but not good enough to pass test#6.
Then I decided to use the straight approach using bool exists[1000000] that indicates whether n is substring. It approach can be done since total length is 10^5, so 10^6 is free for sure.

Since we know several approaches sometimes we use more complex first :)

cool.

good idea!