Loop

Arrays & Hashing

Hash maps and sets as the universal O(1) lookup weapon, plus prefix/suffix products.

0 of 7 lessons complete · 152 min total

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  1. Hash Maps: Trading Space for SpeedWhen an O(n^2) scan is secretly just asking 'does X exist / how many so far' — counting, complements, grouping by signature keys, and set membership.Lesson · 15 minNot completed
  2. Watch a Hash Map WorkFrequency counting and complement lookup animated.Animation · 9 minNot completed
  3. Prefix & Suffix Running TotalsPrecomputing cumulative values to answer range questions instantly — the trick behind Product of Array Except Self.Animation · 10 minNot completed
  4. Practice: Hashing WarmupsSet membership, frequency comparison, and the classic complement lookup.easy×33 problems · 0 solvedPractice · 30 minNot completed
  5. Practice: Hash Keys & BucketsDesigning the right hash key: char-count signatures, frequency buckets, and length-prefix encoding.medium×33 problems · 0 solvedPractice · 40 minNot completed
  6. Practice: Beyond the BasicsPrefix/suffix products, multi-set validation, and the sequence-start trick.medium×33 problems · 0 solvedPractice · 40 minNot completed
  7. Arrays & Hashing CheckpointChoosing hash keys, prefix-sum applications, and spotting hidden O(1)-lookup opportunities.Checkpoint · 8 minNot completed