Hash Table Data Structure
A Hash Table maps string/number keys to array index buckets using a mathematical Hash Function, delivering average O(1) key lookups.
Hash Table Key Lookup & Insertion Step-by-Step
Compute Hash Code
Pass string key 'cat' to hash function to compute integer ASCII code total.
Hash('cat') = ('c':99 + 'a':97 + 't':116) = 312Map Code to Bucket Array Index
Apply modulo arithmetic using array capacity: index = hashCode % capacity.
Index = 312 % 10 = Bucket 2Store Key-Value Pair in Bucket
Write key-value entry ('cat', 42) into Bucket 2. If occupied, handle collision via linked list.
Bucket 2 -> [ ('cat': 42) ]Real-world analogy: Library Index Catalog
Books are assigned letter codes. Instead of scanning all shelves, you calculate the code index to walk directly to the exact shelf slot.
- Hash Function= Converts input keys into target integer array bucket indices.
- Collision= Occurs when two different keys map to the same bucket index.
Operations explained
Complexity analysis
1 step (Constant)
O(1) Average Bucket Access
O(N) Bucket Storage
Memory growth rate as N expands.
Relative efficiency rating for large N.
| Operation | Time Complexity | Space Complexity |
|---|---|---|
| Search | O(1) Avg | O(N) |
| Insertion | O(1) Avg | O(N) |
| Deletion | O(1) Avg | O(N) |
Code implementations
const map = new Map();
map.set("score", 99);
const score = map.get("score");Real-world applications
Database Caching
Stores key-value lookup caches in Memcached/Redis.
Duplicate Checking
Detects unique user handles instantly.
Interview questions
Topic Knowledge Test & Assessment
Hash Table Knowledge & Skill Test
Validate your conceptual understanding, operation mechanics, and core concepts of Hash Table.
Topic Metadata
When hash collisions occur, hash tables use separate chaining (linked list buckets) or open addressing to resolve collisions!