Serialize a key-value store to disk when keys and values can contain any character, including your delimiter
No JSON libraries allowed, and the test data contains commas, newlines, and your escape character itself. Length-prefix encoding solves it in fifteen lines, and knowing why it beats escaping is the actual interview.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
No JSON libraries allowed, and the test data contains commas, newlines, and your escape character itself. Length-prefix encoding solves it in fifteen lines, and knowing why it beats escaping is the actual interview.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
