I recently encountered Problem-B BinCoin from 2022-2023 ICPC, NERC, Northern Eurasia Onsite (Unrated, Online Mirror, ICPC Rules, Teams Preferred) while practicing random 2200 problems.

The problem is based on a binary rooted tree generated by the jury, and a random in-order traversal of that tree. I was sure my solution to this problem was reliable. But it seemed to RTE on test-16. I tried several methods to circumvent the situation to no avail.

Today I attempted to stress test my solution by generating random binary rooted trees, with random traversals.
While validating I mistakenly entered an even number for the number of nodes and realized it immediately.
I couldn't find any valid test case which would reliably thwart my approach.
So I went ahead and put an assertion for the input to see if the input is incorrect by RTE.
To my surprise the system AC's my solution!