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Coding problems

Each problem asks you to decide what the program should do before revealing a solution. Compare approaches, trace state, test edge cases, and explain the complexity in your own words.

BeginnerReviewed 2026-08-17

Two Sum with Indices

Learn the two-sum pattern by predicting state, tracing a hash map, comparing brute force, and testing edge cases in Python and TypeScript.

arrays
hash maps
complements
single-pass algorithms
time complexity

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