Ch 9 · Hash Tables — Instant Lookups · Data Structures & Algorithms

Topic 9 of 10 in Data Structures & Algorithms — Foundations — 2 lessons.

Why dict Is So Fast

A hash table turns a key into a number (a hash) and uses it as an address — so finding a value takes O(1) on average, no scanning. Python's dict and set are hash tables, which is why x in my_set is so fast.

Collisions (The Honest Footnote)

Sometimes two keys produce the same address — a collision. Hash tables handle this by keeping a small bucket of entries at each address and checking within it. Good hashing keeps buckets tiny, so lookups stay O(1) on average (worst case O(n), but rare).

All topics in Data Structures & Algorithms Beginner

1. Thinking Like a Computer Scientist
2. Arrays & Lists — The Workhorse
3. Stacks — Last In, First Out
4. Queues — First In, First Out
5. Linked Lists — Nodes on a Chain
6. Searching — Finding the Needle
7. Sorting — Putting Things in Order
8. Recursion — Functions That Call Themselves
9. Hash Tables — Instant Lookups
10. Mini-Projects & Practice