Data Structures
B2.2 - Data structures
Overview
Every program needs to store collections of data. This section covers fundamental data structures: from simple arrays to abstract structures like stacks and queues.
| # | Topic | Syllabus | Key Concepts | Level |
|---|---|---|---|---|
| 1 | 1D Arrays | B2.2.2 | Static structure; fixed size, direct index access | SL + HL |
| 2 | 2D Arrays | B2.2.2 | Static structure; rows and columns (grid/table) | SL + HL |
| 3 | ArrayList | B2.2.2 | Dynamic structure; grows and shrinks automatically | SL + HL |
| 4 | Stacks | B2.2.3 | Abstract structure; Last In, First Out (LIFO) | SL + HL |
| 5 | Queues | B2.2.4 | Abstract structure; First In, First Out (FIFO) | SL + HL |
Choose a topic above for worked examples, quizzes and practice exercises.
Choosing the Right Structure
| Situation | Best choice |
|---|---|
| Fixed number of items, fast index access | Array |
| Number of items changes at runtime | ArrayList |
| Need LIFO (undo, backtracking) | Stack |
| Need FIFO (order matters, job queue) | Queue |
| Tabular data (grid, board, matrix) | 2D Array |
Static vs Dynamic Structures
| Feature | Static (Array) | Dynamic (ArrayList; Java’s Stack and LinkedList queue) |
|---|---|---|
| Size | Fixed at creation | Grows or shrinks at runtime |
| Memory | Allocated once | Allocated as needed |
| Access | Direct by index | Depends on type |
| Speed | Very fast | Slight overhead |
The key insight: static structures are simpler and faster when you know the size in advance. Dynamic structures are necessary when size changes at runtime.