Section 9.3 The Graph Abstract Data Type
The graph abstract data type (ADT) is defined as follows:
Graph()
creates a new, empty graph.
addVertex(vert)
adds an instance of Vertex
to the graph.
addEdge(fromVert, toVert)
Adds a new, directed edge to the graph that connects two vertices.
addEdge(fromVert, toVert, weight)
Adds a new, weighted, directed edge to the graph that connects two vertices.
getVertex(vertKey)
finds the vertex in the graph named vertKey
.
getVertices()
returns the list of all vertices in the graph.
in
returns True
for a statement of the form vertex in graph
, if the given vertex is in the graph, False
otherwise.
Beginning with the formal definition for a graph there are several ways we can implement the graph ADT in Python. We will see that there are trade-offs in using different representations to implement the ADT described above. There are two well-known implementations of a graph, the adjacency matrix and the adjacency list. We will explain both of these options, and then implement one as a Python class.
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