Hash Maps & Sets

Beginner

Hash maps are the backbone of caching, indexing, and deduplication in real systems. Learn to reach for O(1) lookups instinctively.

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Foundations

Two SumValue → Index Map

Valid AnagramCounter Comparison

Group AnagramsSorted Key Grouping

Top K Frequent ElementsCounter + heapq

Longest Consecutive SequenceSet Lookup

Core

Encode and Decode StringsLength Prefix

Subarray Sum Equals KPrefix Sum + Map

Isomorphic StringsBi-directional Map

LRU CacheOrderedDict

Design HashMapChaining