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DSA learning path

Hashing

Hash maps, sets, frequency counting and constant-time lookup.

Start with Contains Duplicate

Problems in this path

  1. Contains Duplicate
    Easy · Hash Set
    Open
  2. Group Anagrams
    Medium · Frequency Key
    Open
  3. Longest Consecutive Sequence
    Hard · Hash Set
    Open
  4. First Unique Character
    Easy · Frequency Map
    Open
  5. Isomorphic Strings
    Easy · Bidirectional Mapping
    Open
  6. Count Subarrays Summing to K
    Medium · Prefix Frequency Map
    Open
  7. Happy Number
    Easy · Seen-State Set
    Open
  8. Word Pattern Bijection
    Easy · Bidirectional Mapping
    Open
  9. Unique Array Intersection
    Easy · Hash Set Intersection
    Open
  10. Four-Array Zero-Sum Count
    Medium · Pair-Sum Hashing
    Open

Read first

Hash Maps and Hash Sets

How a hash function turns a key into an array index, what happens when two keys collide, and why lookups take O(1) on average.

16 min read