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65 lines
1.9 KiB
65 lines
1.9 KiB
7 months ago
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"""
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File: graph_bfs.py
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Created Time: 2023-02-23
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Author: krahets (krahets@163.com)
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"""
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import sys
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from pathlib import Path
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sys.path.append(str(Path(__file__).parent.parent))
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from modules import Vertex, vals_to_vets, vets_to_vals
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from collections import deque
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from graph_adjacency_list import GraphAdjList
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def graph_bfs(graph: GraphAdjList, start_vet: Vertex) -> list[Vertex]:
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"""Breadth-first traversal"""
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# Use adjacency list to represent the graph, to obtain all adjacent vertices of a specified vertex
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# Vertex traversal sequence
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res = []
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# Hash set, used to record visited vertices
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visited = set[Vertex]([start_vet])
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# Queue used to implement BFS
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que = deque[Vertex]([start_vet])
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# Starting from vertex vet, loop until all vertices are visited
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while len(que) > 0:
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vet = que.popleft() # Dequeue the vertex at the head of the queue
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res.append(vet) # Record visited vertex
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# Traverse all adjacent vertices of that vertex
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for adj_vet in graph.adj_list[vet]:
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if adj_vet in visited:
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continue # Skip already visited vertices
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que.append(adj_vet) # Only enqueue unvisited vertices
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visited.add(adj_vet) # Mark the vertex as visited
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# Return the vertex traversal sequence
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return res
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"""Driver Code"""
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if __name__ == "__main__":
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# Initialize undirected graph
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v = vals_to_vets([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
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edges = [
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[v[0], v[1]],
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[v[0], v[3]],
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[v[1], v[2]],
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[v[1], v[4]],
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[v[2], v[5]],
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[v[3], v[4]],
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[v[3], v[6]],
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[v[4], v[5]],
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[v[4], v[7]],
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[v[5], v[8]],
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[v[6], v[7]],
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[v[7], v[8]],
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]
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graph = GraphAdjList(edges)
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print("\nAfter initialization, the graph is")
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graph.print()
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# Breadth-first traversal
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res = graph_bfs(graph, v[0])
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print("\nBreadth-first traversal (BFS) vertex sequence is")
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print(vets_to_vals(res))
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