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Level: Staff-Level
Round: Onsite · Type: Multiple Types · Difficulty: 5/10 · Duration: 300 min · Interviewer: Unfriendly
Topics: Binary Search, Lowest Common Ancestor, Backtracking, Dynamic Programming, System Design, WebSockets, SSE, Behavioral Questions
Location: San Francisco Bay Area
Interview date: 2026-01-15
My onsite interview consisted of several rounds. In the first coding round, the interviewer was lenient and emphasized speed. I was asked to solve a variant of the Find Peak Element problem using binary search: find an element smaller than its neighbors. I also had to find the Lowest Common Ancestor.
In the AI coding round, I had to find the largest subset containing unique characters. I provided a backtracking solution first. For the second test case, I optimized the path by returning if I had found 26 characters. The third test case required dynamic programming with state tracking, recording the previous state's bitmap and subset to reconstruct the path. I was told to pre-process the test cases to handle anagrams, such as 'abc' and 'cba,' as duplicates using a visited set. The focus was on understanding and reasoning about AI-generated code.
The first system design question was to design Instagram, focusing on the timeline feature and personalization. The second system design question involved designing a 1:1 chat app. I used WebSockets to maintain presence and socket connection mapping but was questioned about not using SSE. I argued that WebSockets allow the client to send heartbeats, facilitating decisions on whether to send to the offline inbox. The interviewer suggested SSE was better due to being more lightweight. When I was asked how to receive messages if the user turned off notifications, I suggested a push and pull mechanism, with notifications disabled messages being pulled. The interviewer disagreed with my approach.
In the behavioral round, the interviewer did not ask conflict resolution questions. Instead, the questions focused on my proudest project, mistakes, and feedback from my manager.