In the latest codeforces Div. 3 contest, my solution for problem D is getting time limit exceeded. The code is written in java and I couldn't figure out the reason. The Problem and my 54157908. I saw some other java code which are accepted that have similar time complexity as my code.

I've tried submitting a solution to problem 1146C — Tree Diameter Submission

But I get Idleness limit exceeded on test 1, I tested my code using Custom Test, but it seems to be working Okay, how can I fix this?