Add the Python codes for the chapter of Graph and Heap (#382)

codes/python/chapter_graph/graph_bfs.py

@@ -0,0 +1,48 @@
+"""
+File: graph_bfs.py
+Created Time: 2023-02-23
+Author: Krahets (krahets@163.com)
+"""
+
+import sys, os.path as osp
+sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
+from include import *
+from graph_adjacency_list import GraphAdjList
+
+""" 广度优先遍历 BFS """
+# 使用邻接表来表示图，以便获取指定顶点的所有邻接顶点
+def graph_bfs(graph: GraphAdjList, start_vet: Vertex) -> List[Vertex]:
+    # 顶点遍历序列
+    res = []
+    # 哈希表，用于记录已被访问过的顶点
+    visited = set([start_vet])
+    # 队列用于实现 BFS
+    que = collections.deque([start_vet])
+    # 以顶点 vet 为起点，循环直至访问完所有顶点
+    while len(que) > 0:
+        vet = que.popleft()  # 队首顶点出队
+        res.append(vet)      # 记录访问顶点
+        # 遍历该顶点的所有邻接顶点
+        for adj_vet in graph.adj_list[vet]:
+            if adj_vet in visited:
+                continue         # 跳过已被访问过的顶点
+            que.append(adj_vet)  # 只入队未访问的顶点
+            visited.add(adj_vet) # 标记该顶点已被访问
+    # 返回顶点遍历序列
+    return res
+
+
+if __name__ == "__main__":
+    """初始化无向图"""
+    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("\n初始化后，图为")
+    graph.print()
+
+    """广度优先遍历 BFS"""
+    res = graph_bfs(graph, v[0])
+    print("\n广度优先遍历（BFS）顶点序列为")
+    print(vets_to_vals(res))