just finished the Bain OA for a data engineering role. sharing because the format is a little different from pure leetcode shops.
the platform: HackerRank. straightforward setup, nothing weird. you get a link, 90 minutes, two problems.
problem 1: a graph traversal question. find all connected components in an undirected graph, return the size of the largest one. classic BFS/DFS. medium difficulty if you've done any graph prep. i solved it in about 25 min.
problem 2: more interesting. a variation on interval merging with a twist on how overlaps were defined. medium-hard. i got a working solution but it wasn't optimal. passed 9/12 test cases.
the catch: the OA is not just about getting the answer. at least for the eng roles, they send a follow-up async question about your approach. one paragraph, recorded video. basically: explain your reasoning for the solution you submitted and any trade-offs. this part surprised me and i wish i'd known about it.
difficulty overall: not hard by FAANG standards. if you're solid on graphs, arrays, and basic DP you'll be fine. they're not trying to filter out everyone who hasn't memorized segment trees.
for context i'm a DE, not a pure SWE, and i passed the OA stage. so the bar isn't set for leetcode grinders specifically. practical problem-solving matters more than optimal time complexity as long as you can explain yourself.
timeline from OA to next step was 10 days in my case.