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/**
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* File: graph_bfs.swift
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* Created Time: 2023-02-21
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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import graph_adjacency_list_target
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import utils
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/* 广度优先遍历 BFS */
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// 使用邻接表来表示图，以便获取指定顶点的所有邻接顶点
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func graphBFS(graph: GraphAdjList, startVet: Vertex) -> [Vertex] {
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// 顶点遍历序列
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var res: [Vertex] = []
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// 哈希表，用于记录已被访问过的顶点
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var visited: Set<Vertex> = [startVet]
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// 队列用于实现 BFS
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var que: [Vertex] = [startVet]
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// 以顶点 vet 为起点，循环直至访问完所有顶点
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while !que.isEmpty {
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let vet = que.removeFirst() // 队首顶点出队
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res.append(vet) // 记录访问顶点
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// 遍历该顶点的所有邻接顶点
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for adjVet in graph.adjList[vet] ?? [] {
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if visited.contains(adjVet) {
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continue // 跳过已被访问过的顶点
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}
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que.append(adjVet) // 只入队未访问的顶点
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visited.insert(adjVet) // 标记该顶点已被访问
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}
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}
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// 返回顶点遍历序列
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return res
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}
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@main
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enum GraphBFS {
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/* Driver Code */
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static func main() {
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/* 初始化无向图 */
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let v = Vertex.valsToVets(vals: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
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let edges = [
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[v[0], v[1]], [v[0], v[3]], [v[1], v[2]], [v[1], v[4]],
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[v[2], v[5]], [v[3], v[4]], [v[3], v[6]], [v[4], v[5]],
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[v[4], v[7]], [v[5], v[8]], [v[6], v[7]], [v[7], v[8]],
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]
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let graph = GraphAdjList(edges: edges)
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print("\n初始化后，图为")
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graph.print()
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/* 广度优先遍历 BFS */
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let res = graphBFS(graph: graph, startVet: v[0])
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print("\n广度优先遍历（BFS）顶点序列为")
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print(Vertex.vetsToVals(vets: res))
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}
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}
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