Step-by-Step Simulations

A simulation problem gives you a set of rules and asks you to step a small world forward, one tick at a time, until something happens. At Hudson River Trading these come up at more than one stage. Two of the three problems below come from the 30-minute technical screen, where the interviewer reads the rules aloud in CoderPad and you don't get any test cases. The third came at the end of a CodeSignal assessment for interns.

The code is usually short, so most bugs come from a rule you heard slightly wrong. Before you write the loop, write down what happens inside a single tick and in what order, then repeat it back to the interviewer. Ask about ties and ordering now, while changing your plan is still cheap.

Then look for the quiet stretches. In two of these problems the state sits idle for long gaps between events. Once a first version runs, a question about jumping over those gaps tends to follow, so keep it in mind from the start. Machine Coding covered building small components. Here the components are tiny, and the work is getting every rule exactly right.

Hudson River TradingPremium lesson · Coding round

The 3 Hudson River Trading problems are below.

1. 1A Premium questionCoding · Medium · Signature problem
2. 2A Premium questionCoding · Medium · Frequently asked
3. 3A Premium questionCoding · Medium

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

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