BlackRock Coding Interview: Aladdin OA

Before a human ever reads your resume closely, BlackRock usually sends an online assessment. It's a timed HackerRank screen of about an hour, typically two coding problems and often a short behavioral prompt. It's the gate that decides whether the rest of the loop happens. The problems sit in the easy to easy-medium band, and that's the trap. Candidates assume gentle difficulty means a relaxed hour, then lose the screen to the clock and the scoring rather than to any single hard algorithm. This lesson covers how you're graded, then works three problems in full at the difficulty the OA hits.

The BlackRock angle

The OA is graded by hidden test cases that award partial credit, and that fact should drive every decision you make in the hour. You do not get a pass or fail on a problem. Your score is proportional to how many of a batch of unseen cases your code clears. Most of them probe the edges: an empty collection, a single element, a target exactly on a boundary, an input large enough that a quadratic loop times out. A clean solution that handles the ordinary case and the obvious edges banks most of the points on a problem even if you never find the elegant optimum. A brilliant approach you are still typing when time expires banks nothing. Prep the fundamentals cold so the standard structure comes out fast. Spend the saved minutes on edges and on the second problem instead of polishing the first once its points are already yours.

What's inside

3 problems, worked step by step
about 30 min

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What candidates walked out with, from 20,000+ reports, forum threads behind logins and write-ups in Chinese. Then solved step by step.

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The Aladdin OA

These took digging.

Know what BlackRock asks before you walk in.