What is the difference between a stack and a queue?

A stack is LIFO—the last element pushed is the first one popped, like a pile of plates. A queue is FIFO—the first element enqueued is the first dequeued, like a checkout line. Stacks are used in recursion and undo operations; queues are used in scheduling and BFS graph traversal.

Why do hash tables have O(1) average lookup?

A hash function converts the key into an integer index, directly pointing to the memory location. As long as the load factor (items ÷ buckets) stays low, collisions are rare and each lookup touches only one or two memory locations. In the worst case with many collisions, lookup degrades to O(n).

When would you choose a linked list over an array?

Linked lists excel when you need frequent insertions or deletions at the head or middle of the list without shifting elements. Arrays provide O(1) random access by index, which linked lists cannot. If you mostly read by position, use an array; if you mostly insert/delete at arbitrary points, a linked list is more efficient.

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📦 Data Structures

Visualise and interact with fundamental data structures. Push/pop a stack, enqueue/dequeue a queue, insert/delete in a linked list, and watch hash collisions resolved by chaining.

Algorithms & AI3DEasy60 FPS

⚙ Under the hood

Interactive visualisations of stacks, queues, linked lists and hash tables — insert, delete and search step by step.

Data StructuresStackQueueHash Table

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install