Python/graphs/breadth_first_search.py

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#!/usr/bin/python
""" Author: OMKAR PATHAK """
from __future__ import annotations
from queue import Queue
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class Graph:
def __init__(self) -> None:
self.vertices: dict[int, list[int]] = {}
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def print_graph(self) -> None:
"""
prints adjacency list representation of graaph
>>> g = Graph()
>>> g.print_graph()
>>> g.add_edge(0, 1)
>>> g.print_graph()
0 : 1
"""
for i in self.vertices:
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print(i, " : ", " -> ".join([str(j) for j in self.vertices[i]]))
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def add_edge(self, from_vertex: int, to_vertex: int) -> None:
"""
adding the edge between two vertices
>>> g = Graph()
>>> g.print_graph()
>>> g.add_edge(0, 1)
>>> g.print_graph()
0 : 1
"""
if from_vertex in self.vertices:
self.vertices[from_vertex].append(to_vertex)
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else:
self.vertices[from_vertex] = [to_vertex]
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def bfs(self, start_vertex: int) -> set[int]:
"""
>>> g = Graph()
>>> g.add_edge(0, 1)
>>> g.add_edge(0, 1)
>>> g.add_edge(0, 2)
>>> g.add_edge(1, 2)
>>> g.add_edge(2, 0)
>>> g.add_edge(2, 3)
>>> g.add_edge(3, 3)
>>> sorted(g.bfs(2))
[0, 1, 2, 3]
"""
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# initialize set for storing already visited vertices
visited = set()
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# create a first in first out queue to store all the vertices for BFS
queue: Queue = Queue()
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# mark the source node as visited and enqueue it
visited.add(start_vertex)
queue.put(start_vertex)
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while not queue.empty():
vertex = queue.get()
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# loop through all adjacent vertex and enqueue it if not yet visited
for adjacent_vertex in self.vertices[vertex]:
if adjacent_vertex not in visited:
queue.put(adjacent_vertex)
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visited.add(adjacent_vertex)
return visited
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if __name__ == "__main__":
from doctest import testmod
testmod(verbose=True)
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g = Graph()
g.add_edge(0, 1)
g.add_edge(0, 2)
g.add_edge(1, 2)
g.add_edge(2, 0)
g.add_edge(2, 3)
g.add_edge(3, 3)
g.print_graph()
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# 0 : 1 -> 2
# 1 : 2
# 2 : 0 -> 3
# 3 : 3
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assert sorted(g.bfs(2)) == [0, 1, 2, 3]