Glossary

What Is Data Structure?

A data structure is a way of organizing and storing data for efficient access and modification. Arrays, linked lists, hash tables, trees, and graphs are fundamental data structures. Choosing the right data structure determines whether an operation takes microseconds or minutes.

How Data Structure Works

Array: O(1) access by index, O(n) search. Hash table: O(1) average lookup by key. Tree: O(log n) sorted operations. Linked list: O(1) insertion at head. Each data structure excels at different operations — choosing the right one is a core programming skill.

Real-world mapping: JavaScript Array for ordered collections, Map/Object for key-value lookup, Set for unique values, and custom trees/graphs for hierarchical or network data.

Why Developers Use Data Structure

Every programmer uses data structures daily — arrays, objects, maps, sets. Understanding their performance characteristics (when to use a Map vs an Array for lookups) separates efficient code from slow code.

Key Concepts

  • Array — Contiguous memory, O(1) index access, O(n) insertion/deletion — the most common data structure
  • Hash Table — Key-value mapping with O(1) average lookup — JavaScript Objects, Python dicts, Java HashMaps
  • Stack — LIFO (Last In, First Out) — undo systems, function call stacks, expression parsing
  • Queue — FIFO (First In, First Out) — task scheduling, breadth-first search, message processing
  • Tree — Hierarchical structure — file systems, DOM, database indexes, decision trees
  • Graph — Nodes connected by edges — social networks, maps, dependency resolution

Common Data Structures

javascript
// Hash Map — O(1) lookup
const users = new Map();
users.set('alice', { role: 'admin' });
users.get('alice'); // O(1) lookup

// Stack — LIFO
const stack = [];
stack.push('a'); stack.push('b');
stack.pop(); // 'b' — last in, first out

// Queue — FIFO
const queue = [];
queue.push('task1'); queue.push('task2');
queue.shift(); // 'task1' — first in, first out

// Set — unique values, O(1) has()
const seen = new Set();
seen.add('url1'); seen.add('url2');
seen.has('url1'); // true — O(1) check

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Frequently Asked Questions

Which data structures should I learn first?

Arrays, hash tables (objects/maps), stacks, and queues. These cover 90% of real-world programming. Then learn trees and graphs for interviews and specialized problems.

Do data structures matter in high-level languages?

Yes. JavaScript Arrays and Objects are data structures with different performance characteristics. Using an Array for lookups when a Map would be O(1) is a common performance mistake.

Related Terms

AlgorithmHash TableLinked ListTreeBig O Notation

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