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Container With Most Water
You're looking for two lines that hold the most water between them. The brute force checks every pair, but interviewers want to see you discover the two-pointer insight: start wide, then shrink inward by moving the shorter line. It's a beautiful example of greedy reasoning that comes up in many optimization problems.
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.