#️⃣ JavaScript Hashing — Topic Index

Hashing maps keys to values using a hash function, enabling O(1) average-time lookups, inserts, and deletes. JavaScript provides Map and Set as built-in hash structures.

Topics Covered

#	Topic	Key Concepts
1	Basics	Map, Set, frequency counting, plain objects
2	Patterns	Two-sum, grouping, prefix sums, sliding window
3	Interview Questions	25 classic problems

Why Hashing?

O(1) average lookup/insert/delete — transforms O(n²) brute force into O(n)
Frequency counting — character/word counts in O(n)
Prefix sums — subarray problems solved with running sum maps
Deduplication — instantly check if element was seen before

Common Patterns

Two-pointer complement lookup — target - x in Map
Frequency map — count occurrences, find majority element
Prefix sum + Map — subarray sum equals k
Sliding window + freq — minimum window substring, anagrams
Set for O(1) membership — consecutive sequences, duplicates