The FDE Case Interview: Structure the Ambiguity (C.A.S.E.)
The open-ended case is the hardest and least familiar round in the Forward Deployed Engineer loop, and the most common reason candidates are rejected is jumping to a solution before scoping the problem. A repeatable structure fixes that.
The C.A.S.E. framework
C.A.S.E. keeps you organized when you are handed something vague like "design a solution for this customer under these constraints." Narrate all four steps out loud; interviewers grade structured reasoning and customer awareness, not a single right answer.
Clarify
Pin down the requirements, users, data, and hard constraints (security, latency, offline) before touching a solution. State your assumptions with rough numbers.
Architect
Sketch the system at a high level, the boxes and arrows from data in to value out.
Solve
Go one level deeper on the core technical piece: the query, the pipeline, the retrieval step.
Evaluate
Name the trade-offs, risks, and how you would measure success. Running out of time before you reach Evaluate is the most common self-inflicted wound.
A short worked example
Say the prompt is: "A logistics customer wants to flag deliveries likely to be late. Design it." A weak answer jumps straight to a model. A strong one walks C.A.S.E. out loud.
Clarify: how late counts as "late", what data exists (GPS pings, historical times, weather), is this a live alert or a nightly report, and who acts on the flag? Architect: ingest tracking events, join to route history, score risk, surface to dispatchers. Solve: go deep on the scoring step, and start with a simple rule (behind schedule at the last checkpoint) before proposing a model, saying why. Evaluate: measure against deliveries that were actually late, watch false positives (dispatchers ignore a noisy alert), and note you would ship the rule first and earn the right to add a model.
What separates a strong case answer
The grade is judgment under ambiguity. Offer two or three options with trade-offs and choose one for a stated reason: "I would pick B because of the compliance constraint" beats a perfect-sounding single answer. Timebox yourself: a few minutes clarifying, most of the time on architecture and the core solve, and always land on Evaluate.
Rung's Scenario Drills rehearse exactly these judgment calls, realistic customer situations where you make the call and get instant feedback on the reasoning.
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Reconcile Two Record Sets
You are given two lists of records, `a` and `b`. Each record is an object with a unique integer `id` (unique within its own list) and an `amount`....
Solve it in your browser →The editor and test runner load right in the page. This is the format FDE coding rounds use.
Practice FDE scenario drills free
Practice FDE scenario drills free →Frequently asked questions
What is the FDE case interview?
An open-ended round where you are handed an ambiguous customer problem and asked to design a solution. It grades structured reasoning, stated assumptions, and the ability to scope a small end-to-end approach, not a single correct answer.
How do I structure an FDE case interview?
Use a repeatable structure like C.A.S.E.: Clarify the requirements and constraints, Architect the system at a high level, Solve the core technical piece in more depth, and Evaluate trade-offs, risks, and success metrics, narrating your thinking throughout.
What is the most common mistake in the FDE case round?
Jumping to a solution before scoping the problem. Clarify assumptions and constraints first, propose the smallest end-to-end approach, then iterate, rather than boiling the ocean.
How is an FDE case interview different from a management-consulting case?
A consulting case is usually market sizing or business strategy. An FDE case is technical: you scope and sketch a real system (data, integration, a pipeline or model) for a customer problem. The shared skill is structured reasoning under ambiguity; the FDE version expects you to go one level into the engineering.