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Permutation in String
Permutation in String is less about the final answer and more about disciplined window bookkeeping. Interviewers love it because it reveals your stateful scanning and your edge-case discipline. Be disciplined about counts and boundaries; most bugs are off-by-one window moves.
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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.