What is a graph?

A graph has vertices and edges.

A graph is a data structure of vertices and edges connecting them. Unlike a tree it can contain cycles.

In a directed graph edges have a direction (A→B); in an undirected one they are bidirectional (A—B). In a weighted graph edges have a cost.

Graphs are used in pathfinding, social networks, dependency resolution.

Directed and undirected

In a directed graph each edge has a direction: A→B means from A to B but not B to A. In an undirected graph A—B can be traversed both ways.

In the adjacency list a directed graph has graph[A] containing only B; an undirected one has both graph[A] and graph[B] containing each other.

Direction is achieved by adding to both sides during insertion.

Write create_graph(). Return an empty adjacency dict. Print {} with print(create_graph()).

Show example solution

def create_graph():
    # Empty graph
    return {}
print(create_graph())

Edge direction

Undirected graph A—B: add B to graph[A] and add A to graph[____]

Show answer

Undirected graph A—B: add B to graph[A] and add A to graph[A]