Meta SWE, ML - E4 , rejected after final loop

Meta SWE, ML - E4, rejected after final loop

Phone Screen

1. A slight variation of moving averages
2. A slight variation of find the peak element

Loop

1. Behavioral - typical questions; this section lasted approximately 40 minutes.
2. Coding round 1 a. Make valid parentheses - remove one character; follow-up - remove "n" characters (the interviewer did not request code for the follow-up, only a description of my approach and rationale). b. Given a list of intervals, find the number that is contained by the maximum number of intervals. [[2,13], [3,5], [1,4], [2,5]] - The answer is 3 because it is contained in 3 intervals. I provided a greedy approach and then a suboptimal O(n^2) approach; I coded the suboptimal solution.
3. Coding round 2 a. Merge sorted arrays without duplicates b. Lowest common ancestor
4. ML system design - design a location recommendation system

I performed to the best of my ability. Interviewers in the first three rounds provided positive feedback, but I did not perform as well in the ML system design round. I believe this round led to the rejection. I did not receive detailed feedback from the recruiter.