It has been a while after my retirement. I just logged in my account and glanced at last round's scoreboard. Oh wait...?
I found there are two different accounts FST on problem F testcase 23 coincidently. And they look similar: check their dfs function.
Submission 1: https://codeforces.com/contest/1610/submission/136662706
Submission 2: https://codeforces.com/contest/1610/submission/136677514
Of course they are both rated in this contest.
Though I did not even read the whole problem statement, I was wondering the answer to the following question:
Should similar FST solutions be regarded as cheating?