57 lines
1.9 KiB
Swift
57 lines
1.9 KiB
Swift
/**
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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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/* Breadth-first traversal */
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// Use adjacency list to represent the graph, to obtain all adjacent vertices of a specified vertex
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func graphBFS(graph: GraphAdjList, startVet: Vertex) -> [Vertex] {
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// Vertex traversal sequence
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var res: [Vertex] = []
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// Hash set, used to record visited vertices
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var visited: Set<Vertex> = [startVet]
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// Queue used to implement BFS
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var que: [Vertex] = [startVet]
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// Starting from vertex vet, loop until all vertices are visited
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while !que.isEmpty {
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let vet = que.removeFirst() // Dequeue the vertex at the head of the queue
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res.append(vet) // Record visited vertex
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// Traverse all adjacent vertices of that vertex
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for adjVet in graph.adjList[vet] ?? [] {
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if visited.contains(adjVet) {
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continue // Skip already visited vertices
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}
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que.append(adjVet) // Only enqueue unvisited vertices
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visited.insert(adjVet) // Mark the vertex as visited
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}
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}
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// Return the vertex traversal sequence
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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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/* Initialize undirected graph */
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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("\nAfter initialization, the graph is")
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graph.print()
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/* Breadth-first traversal */
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let res = graphBFS(graph: graph, startVet: v[0])
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print("\nBreadth-first traversal (BFS) vertex sequence is")
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print(Vertex.vetsToVals(vets: res))
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}
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}
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