After the recruiter screening, I had a 1:1 coding session with an engineer. I was given a LeetCode hard problem. I actually solved the problem in the interview with all test cases passing (verified the solution by copy-pasting it onto LeetCode), but I still received a rejection.

Their standards seem unrealistic. The expectation is to write the best code without mistakes on the first try. Fixing edge cases and improving code subsequently after writing the initial code is seen as a concern.

I am pretty sure if the tables were turned, the engineer himself couldn't solve the problem.

LeetCode hard problems related to trees.