breadth_first_search.py

#!/usr/bin/python
# encoding=utf8

""" Author: OMKAR PATHAK """


class Graph:
    def __init__(self):
        self.vertex = {}

    # for printing the Graph vertexes
    def printGraph(self):
        for i in self.vertex.keys():
            print(i, " -> ", " -> ".join([str(j) for j in self.vertex[i]]))

    # for adding the edge beween two vertexes
    def addEdge(self, fromVertex, toVertex):
        # check if vertex is already present,
        if fromVertex in self.vertex.keys():
            self.vertex[fromVertex].append(toVertex)
        else:
            # else make a new vertex
            self.vertex[fromVertex] = [toVertex]

    def BFS(self, startVertex):
        # Take a list for stoting already visited vertexes
        visited = [False] * len(self.vertex)

        # create a list to store all the vertexes for BFS
        queue = []

        # mark the source node as visited and enqueue it
        visited[startVertex] = True
        queue.append(startVertex)

        while queue:
            startVertex = queue.pop(0)
            print(startVertex, end=" ")

            # mark all adjacent nodes as visited and print them
            for i in self.vertex[startVertex]:
                if visited[i] == False:
                    queue.append(i)
                    visited[i] = True


if __name__ == "__main__":
    g = Graph()
    g.addEdge(0, 1)
    g.addEdge(0, 2)
    g.addEdge(1, 2)
    g.addEdge(2, 0)
    g.addEdge(2, 3)
    g.addEdge(3, 3)

    g.printGraph()
    print("BFS:")
    g.BFS(2)

    # OUTPUT:
    # 0  ->  1 -> 2
    # 1  ->  2
    # 2  ->  0 -> 3
    # 3  ->  3
    # BFS:
    # 2 0 3 1