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64 lines
1.8 KiB
Python
64 lines
1.8 KiB
Python
"""
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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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"""廣度優先走訪"""
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# 使用鄰接表來表示圖，以便獲取指定頂點的所有鄰接頂點
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# 頂點走訪序列
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res = []
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# 雜湊集合，用於記錄已被訪問過的頂點
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visited = set[Vertex]([start_vet])
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# 佇列用於實現 BFS
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que = deque[Vertex]([start_vet])
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# 以頂點 vet 為起點，迴圈直至訪問完所有頂點
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while len(que) > 0:
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vet = que.popleft() # 佇列首頂點出隊
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res.append(vet) # 記錄訪問頂點
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# 走訪該頂點的所有鄰接頂點
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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 # 跳過已被訪問的頂點
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que.append(adj_vet) # 只入列未訪問的頂點
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visited.add(adj_vet) # 標記該頂點已被訪問
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# 返回頂點走訪序列
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return res
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"""Driver Code"""
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if __name__ == "__main__":
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# 初始化無向圖
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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("\n初始化後，圖為")
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graph.print()
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# 廣度優先走訪
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res = graph_bfs(graph, v[0])
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print("\n廣度優先走訪（BFS）頂點序列為")
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print(vets_to_vals(res))
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