Build a Top-Three Referral Leaderboard from Chronological Events

Company: Robinhood

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Onsite

Overview: Build a referral leaderboard from chronological referrer and referred-user arrays, counting every direct and downstream referral. The prompt returns the top three eligible users with deterministic count and username ordering, matching a DFS-and-memo solution over the referral forest.

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