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Graph list patch (#4113)
* new implementation for adjacency list graph * add example code for undirected graph * reduce length to 88 columns max to fix build errors7 * fix pre commit issues * replace print_list method with __str__ * return object in add_edge method to enable fluent syntax * improve class docstring and include doctests * add end of file line * fix pre-commit issues * remove __str__ method * trigger build * Update graph_list.py * Update graph_list.py Co-authored-by: gnc <chidieberen1999@gmail.com> Co-authored-by: Christian Clauss <cclauss@me.com>
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Nwachukwu Chidiebere Godwin
GitHub
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#!/usr/bin/python
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#!/usr/bin/env python3
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# Author: OMKAR PATHAK
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# Author: OMKAR PATHAK, Nwachukwu Chidiebere
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# We can use Python's dictionary for constructing the graph.
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# Use a Python dictionary to construct the graph.
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from pprint import pformat
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class AdjacencyList:
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def __init__(self):
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self.adj_list = {}
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class GraphAdjacencyList:
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"""
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Adjacency List type Graph Data Structure that accounts for directed and undirected
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Graphs. Initialize graph object indicating whether it's directed or undirected.
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def add_edge(self, from_vertex: int, to_vertex: int) -> None:
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# check if vertex is already present
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if from_vertex in self.adj_list:
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self.adj_list[from_vertex].append(to_vertex)
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else:
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self.adj_list[from_vertex] = [to_vertex]
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Directed graph example:
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>>> d_graph = GraphAdjacencyList()
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>>> d_graph
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{}
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>>> d_graph.add_edge(0, 1)
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{0: [1], 1: []}
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>>> d_graph.add_edge(1, 2).add_edge(1, 4).add_edge(1, 5)
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{0: [1], 1: [2, 4, 5], 2: [], 4: [], 5: []}
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>>> d_graph.add_edge(2, 0).add_edge(2, 6).add_edge(2, 7)
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{0: [1], 1: [2, 4, 5], 2: [0, 6, 7], 4: [], 5: [], 6: [], 7: []}
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>>> print(d_graph)
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{0: [1], 1: [2, 4, 5], 2: [0, 6, 7], 4: [], 5: [], 6: [], 7: []}
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>>> print(repr(d_graph))
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{0: [1], 1: [2, 4, 5], 2: [0, 6, 7], 4: [], 5: [], 6: [], 7: []}
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def print_list(self) -> None:
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for i in self.adj_list:
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print((i, "->", " -> ".join([str(j) for j in self.adj_list[i]])))
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Undirected graph example:
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>>> u_graph = GraphAdjacencyList(directed=False)
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>>> u_graph.add_edge(0, 1)
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{0: [1], 1: [0]}
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>>> u_graph.add_edge(1, 2).add_edge(1, 4).add_edge(1, 5)
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{0: [1], 1: [0, 2, 4, 5], 2: [1], 4: [1], 5: [1]}
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>>> u_graph.add_edge(2, 0).add_edge(2, 6).add_edge(2, 7)
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{0: [1, 2], 1: [0, 2, 4, 5], 2: [1, 0, 6, 7], 4: [1], 5: [1], 6: [2], 7: [2]}
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>>> u_graph.add_edge(4, 5)
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{0: [1, 2],
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1: [0, 2, 4, 5],
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2: [1, 0, 6, 7],
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4: [1, 5],
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5: [1, 4],
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6: [2],
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7: [2]}
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>>> print(u_graph)
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{0: [1, 2],
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1: [0, 2, 4, 5],
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2: [1, 0, 6, 7],
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4: [1, 5],
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5: [1, 4],
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6: [2],
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7: [2]}
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>>> print(repr(u_graph))
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{0: [1, 2],
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1: [0, 2, 4, 5],
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2: [1, 0, 6, 7],
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4: [1, 5],
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5: [1, 4],
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6: [2],
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7: [2]}
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"""
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def __init__(self, directed: bool = True):
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"""
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Parameters:
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directed: (bool) Indicates if graph is directed or undirected. Default is True.
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"""
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self.adj_list = {} # dictionary of lists
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self.directed = directed
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def add_edge(self, source_vertex: int, destination_vertex: int) -> object:
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"""
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Connects vertices together. Creates and Edge from source vertex to destination
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vertex.
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Vertices will be created if not found in graph
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"""
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if not self.directed: # For undirected graphs
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# if both source vertex and destination vertex are both present in the
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# adjacency list, add destination vertex to source vertex list of adjacent
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# vertices and add source vertex to destination vertex list of adjacent
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# vertices.
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if source_vertex in self.adj_list and destination_vertex in self.adj_list:
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self.adj_list[source_vertex].append(destination_vertex)
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self.adj_list[destination_vertex].append(source_vertex)
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# if only source vertex is present in adjacency list, add destination vertex
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# to source vertex list of adjacent vertices, then create a new vertex with
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# destination vertex as key and assign a list containing the source vertex
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# as it's first adjacent vertex.
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elif source_vertex in self.adj_list:
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self.adj_list[source_vertex].append(destination_vertex)
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self.adj_list[destination_vertex] = [source_vertex]
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# if only destination vertex is present in adjacency list, add source vertex
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# to destination vertex list of adjacent vertices, then create a new vertex
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# with source vertex as key and assign a list containing the source vertex
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# as it's first adjacent vertex.
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elif destination_vertex in self.adj_list:
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self.adj_list[destination_vertex].append(source_vertex)
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self.adj_list[source_vertex] = [destination_vertex]
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# if both source vertex and destination vertex are not present in adjacency
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# list, create a new vertex with source vertex as key and assign a list
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# containing the destination vertex as it's first adjacent vertex also
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# create a new vertex with destination vertex as key and assign a list
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# containing the source vertex as it's first adjacent vertex.
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else:
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self.adj_list[source_vertex] = [destination_vertex]
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self.adj_list[destination_vertex] = [source_vertex]
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else: # For directed graphs
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# if both source vertex and destination vertex are present in adjacency
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# list, add destination vertex to source vertex list of adjacent vertices.
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if source_vertex in self.adj_list and destination_vertex in self.adj_list:
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self.adj_list[source_vertex].append(destination_vertex)
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# if only source vertex is present in adjacency list, add destination
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# vertex to source vertex list of adjacent vertices and create a new vertex
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# with destination vertex as key, which has no adjacent vertex
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elif source_vertex in self.adj_list:
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self.adj_list[source_vertex].append(destination_vertex)
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self.adj_list[destination_vertex] = []
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# if only destination vertex is present in adjacency list, create a new
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# vertex with source vertex as key and assign a list containing destination
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# vertex as first adjacent vertex
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elif destination_vertex in self.adj_list:
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self.adj_list[source_vertex] = [destination_vertex]
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# if both source vertex and destination vertex are not present in adjacency
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# list, create a new vertex with source vertex as key and a list containing
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# destination vertex as it's first adjacent vertex. Then create a new vertex
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# with destination vertex as key, which has no adjacent vertex
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else:
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self.adj_list[source_vertex] = [destination_vertex]
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self.adj_list[destination_vertex] = []
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return self
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def __repr__(self) -> str:
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return pformat(self.adj_list)
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if __name__ == "__main__":
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al = AdjacencyList()
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al.add_edge(0, 1)
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al.add_edge(0, 4)
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al.add_edge(4, 1)
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al.add_edge(4, 3)
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al.add_edge(1, 0)
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al.add_edge(1, 4)
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al.add_edge(1, 3)
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al.add_edge(1, 2)
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al.add_edge(2, 3)
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al.add_edge(3, 4)
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import doctest
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al.print_list()
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# OUTPUT:
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# 0 -> 1 -> 4
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# 1 -> 0 -> 4 -> 3 -> 2
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# 2 -> 3
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# 3 -> 4
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# 4 -> 1 -> 3
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doctest.testmod()
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