I passed problem C of round 980 (Div 1) with a sketchy code that I wrote: https://codeforces.net/contest/2023/submission/300471200

The code has a fast and slow pointer. Set an initial value called match to 0. If a[fast%n] != b[slow%n], increase fast by 1, and set match to 0. Otherwise, increase fast and slow both by 1, and increase match by 1. If fast is greater than slow by n, then a is not a cycle of b. Otherwise, if match is n, then a is a cycle of b.

I would really appreciate it if someone could send me either a test case that TLEs this code, or the proof of why this code works. Thanks.