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Intermediate Topic 28 of 52 Data Structures

Adjacency List

Graph storage keeping each vertex's neighbors in a list.

How it works

Each vertex keeps a list of its neighbors, using O(V + E) memory and giving fast iteration over neighbors, ideal for sparse graphs.

Where it is used

BFS, DFS and Dijkstra implementations.

Common pitfall

Checking whether a specific edge exists takes O(degree) unless neighbors are stored in a set.

Where it fits in the course

Adjacency List is topic 28 of 52 in Data Structures, rated Intermediate. It follows Graphs. The next topic is Adjacency Matrix.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Data Structures quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Adjacency List?
Graph storage keeping each vertex's neighbors in a list. It belongs to Data Structures and is an intermediate-level topic.
Where do people use Adjacency List?
BFS, DFS and Dijkstra implementations.
What is the most common mistake with Adjacency List?
Checking whether a specific edge exists takes O(degree) unless neighbors are stored in a set.
What should I learn before this topic?
Start with Graphs, the topic just before it in Data Structures.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Data Structures quiz.
Is Adjacency List hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Adjacency List?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Adjacency List?
Graphs, Adjacency Matrix, Fenwick Trees are closely connected. The full list is in the related topics section of this page.
What should I study after Adjacency List?
Continue with Adjacency Matrix, the next topic in Data Structures.

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