Tries & Class Design

In these problems you write a class, and then the grader or interviewer runs a long stream of calls against it. What matters is the cost of each operation over that whole sequence, so a design that makes the common call slow can pass a short test and fail a long one. The order book comes up most. That makes sense, since Citadel Securities quotes against live order books all day, and engineers at the hedge fund use the same terms when they talk about markets. The trie problems come from phone screens, where building the basic structure is the warm-up and most of the round goes to follow-ups.

Before you write any fields, list the operations and estimate how often each one runs. On an order book, cancels outnumber fills on a live feed. A cancel that walks a whole price level is a bug. On an autocomplete, keystrokes outnumber commits, so store the top three results in the nodes.

CitadelPremium lesson · Coding round

The 3 Citadel problems are below.

1. 1A Premium questionCoding · Hard · Signature problem
2. 2A Premium questionCoding · Medium
3. 3A Premium questionCoding · Hard

Each with hints, the follow-up and a tested solution.

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