Validate balanced parentheses/brackets, and explain the stack pattern.
A warm-up that tests for the stack instinct. Interviewers look for recognizing that last-opened-first-closed maps onto a stack, plus handling the edge cases (leftover opens, early close). The pattern follows.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
A warm-up that tests for the stack instinct. Interviewers look for recognizing that last-opened-first-closed maps onto a stack, plus handling the edge cases (leftover opens, early close). The pattern follows.
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.
