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Lesson 8 — Graph as adjacency list
Graphs as adjacency lists
A graph is a set of nodes joined by edges — friends in a social network, cities joined by roads. The simplest way to store it is an adjacency list: a dict mapping each node to the list of its neighbours. For an undirected graph (roads work both ways) each edge a–b is added twice: b to a's list and a to b's.
graph = {"A": ["B"], "B": ["A"]}
The number of neighbours a node has is its degree.
Why it matters: this dict-of-lists is the starting point for every graph algorithm (BFS, DFS, Dijkstra).
Want it another way?
Task
For each edge add both directions. Expected: each node with its neighbours and degree.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
Test your knowledge
Test your knowledgeA quick 3-question quiz on this lesson — instant feedback.