Stage 2 of 8 · 6 lessons · ~2 months

Arrays, hashing, linked lists, stacks and queues

Learn the linear structures and hash maps that most problems are built on, and exactly what your language gives you for each. Counting, grouping and lookup problems all start here.

Start: Arrays, dynamic arrays and strings

Lessons· one lesson for each topic, in this order

Start with· follow one of these

CoursePaid
Grokking Data Structures & Algorithms for Coding Interviews
Design Gurus · Beginner · Subscription
Each structure from first principles, with solutions in Python, Java, C++ and JavaScript
CourseFree
MIT 6.006 Introduction to Algorithms
MIT OpenCourseWare · Intermediate
Free: lectures 2 and 4 cover dynamic arrays, linked lists, sets and hashing

Practise

Design Gurus Problem Set
Free problems filtered by data structure: arrays, hash tables, linked lists, stacks
HackerEarth Practice
The Data Structures track has short notes and graded easy problems per topic

Keep handy

cppreference.com
Containers library: vector, unordered_map, deque and stack, with complexity for each call

Also worth your time

Choosing the Right Data Structure: A Comprehensive Decision Guide (opens in a new tab)Read
How to pick a structure from the operations a problem needs

Before moving on: Implement a dynamic array, a linked list and a hash map with chaining from scratch, state the Big-O of every operation, then solve 25 easy and 5 medium array, string, hash map, linked list and stack problems.

Tauseef's advice

Build each structure yourself once, even though your language ships one, because that is where the costs stop being facts you memorised. When a problem says "have we seen this before" or "how many times", reach for a hash map first.