1+ from queue import Queue
2+ 3+ class Graph :
4+ # Constructor
5+ def __init__ (self , num_of_nodes , directed = True ):
6+ self .m_num_of_nodes = num_of_nodes
7+ self .m_nodes = range (self .m_num_of_nodes )
8+ 9+ # Directed or Undirected
10+ self .m_directed = directed
11+ 12+ # Graph representation - Adjacency list
13+ # We use a dictionary to implement an adjacency list
14+ self .m_adj_list = {node : set () for node in self .m_nodes }
15+ 16+ # Add edge to the graph
17+ def add_edge (self , node1 , node2 , weight = 1 ):
18+ self .m_adj_list [node1 ].add ((node2 , weight ))
19+ 20+ if not self .m_directed :
21+ self .m_adj_list [node2 ].add ((node1 , weight ))
22+ 23+ # Print the graph representation
24+ def print_adj_list (self ):
25+ for key in self .m_adj_list .keys ():
26+ print ("node" , key , ": " , self .m_adj_list [key ])
27+ 28+ def bfs (self , start_node , target_node ):
29+ # Set of visited nodes to prevent loops
30+ visited = set ()
31+ queue = Queue ()
32+ 33+ # Add the start_node to the queue and visited list
34+ queue .put (start_node )
35+ visited .add (start_node )
36+ 37+ # start_node has not parents
38+ parent = dict ()
39+ parent [start_node ] = None
40+ 41+ # Perform step 3
42+ path_found = False
43+ while not queue .empty ():
44+ current_node = queue .get ()
45+ if current_node == target_node :
46+ path_found = True
47+ break
48+ 49+ for (next_node , weight ) in self .m_adj_list [current_node ]:
50+ if next_node not in visited :
51+ queue .put (next_node )
52+ parent [next_node ] = current_node
53+ visited .add (next_node )
54+ 55+ # Path reconstruction
56+ path = []
57+ if path_found :
58+ path .append (target_node )
59+ while parent [target_node ] is not None :
60+ path .append (parent [target_node ])
61+ target_node = parent [target_node ]
62+ path .reverse ()
63+ return path
64+ 65+ def bfs_traversal (self , start_node ):
66+ visited = set ()
67+ queue = Queue ()
68+ queue .put (start_node )
69+ visited .add (start_node )
70+ 71+ while not queue .empty ():
72+ current_node = queue .get ()
73+ print (current_node , end = " " )
74+ for (next_node , weight ) in self .m_adj_list [current_node ]:
75+ if next_node not in visited :
76+ queue .put (next_node )
77+ visited .add (next_node )
78+ 79+ def main ():
80+ # Testing the `bfs()` method
81+ graph1 = Graph (6 , directed = False )
82+ 83+ graph1 .add_edge (0 , 1 )
84+ graph1 .add_edge (0 , 2 )
85+ graph1 .add_edge (0 , 3 )
86+ graph1 .add_edge (0 , 4 )
87+ graph1 .add_edge (1 , 2 )
88+ graph1 .add_edge (2 , 3 )
89+ graph1 .add_edge (2 , 5 )
90+ graph1 .add_edge (3 , 4 )
91+ graph1 .add_edge (3 , 5 )
92+ graph1 .add_edge (4 , 5 )
93+ 94+ graph1 .print_adj_list ()
95+ 96+ path = []
97+ path = graph1 .bfs (0 , 5 )
98+ print (path )
99+ 100+ # Testing the `bfs_traversal()` method
101+ graph2 = Graph (5 , directed = False )
102+ 103+ graph2 .add_edge (0 , 1 )
104+ graph2 .add_edge (0 , 2 )
105+ graph2 .add_edge (1 , 2 )
106+ graph2 .add_edge (1 , 4 )
107+ graph2 .add_edge (2 , 3 )
108+ 109+ graph2 .bfs_traversal (0 )
110+ 111+ if __name__ == "__main__" :
112+ main ()
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