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Asteroid Collision
This is a stack/invariant problem: once your stack represents the right thing, the rest is routine. Interviewers love it because it reveals your stack invariants and your edge-case discipline. The classic mistake is not being clear about what your stack represents at each step.
Learn this pattern
Arrays and Hashing Interview Questions
Arrays and hashing problems are about fast lookup choices: set for membership, map for attached state, and buckets when counts are bounded. Reach for this family when brute force compares too many pairs or when you need to remember what you saw earlier in one pass.
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Arrays and Hashing Interview Questions gives you a useful next rep while you are still on your phone.