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hello-algo/en/codes/python/chapter_graph/graph_bfs.py
Yudong Jin 2778a6f9c7 Translate all code to English (#1836)
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2025-12-31 07:44:52 +08:00

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Python

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