mirror of
https://github.com/krahets/hello-algo.git
synced 2026-11-10 16:00:36 +08:00
14c314c08c
* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
65 lines
1.9 KiB
Python
65 lines
1.9 KiB
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"""
|
|
# Represent the graph with an adjacency list to access all neighbors of a given vertex
|
|
# Vertex traversal sequence
|
|
res = []
|
|
# Hash set recording visited vertices
|
|
visited = set[Vertex]([start_vet])
|
|
# Use a queue to implement BFS
|
|
que = deque[Vertex]([start_vet])
|
|
# Starting from start_vet, loop until all reachable vertices have been visited
|
|
while len(que) > 0:
|
|
vet = que.popleft() # Dequeue the front vertex
|
|
res.append(vet) # Record the visited vertex
|
|
# Traverse all neighbors of this vertex
|
|
for adj_vet in graph.adj_list[vet]:
|
|
if adj_vet in visited:
|
|
continue # Skip vertices that have already been visited
|
|
que.append(adj_vet) # Enqueue only unvisited vertices
|
|
visited.add(adj_vet) # Mark this vertex as visited
|
|
# Return the vertex traversal sequence
|
|
return res
|
|
|
|
|
|
"""Driver code"""
|
|
if __name__ == "__main__":
|
|
# Initialize the 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("\nGraph after initialization:")
|
|
graph.print()
|
|
|
|
# Breadth-first traversal
|
|
res = graph_bfs(graph, v[0])
|
|
print("\nVertex sequence from breadth-first traversal (BFS):")
|
|
print(vets_to_vals(res))
|