65 lines
2.0 KiB
Kotlin
65 lines
2.0 KiB
Kotlin
/**
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* File: graph_bfs.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_graph
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import utils.Vertex
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import java.util.*
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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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fun graphBFS(graph: GraphAdjList, startVet: Vertex): MutableList<Vertex?> {
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// Vertex traversal sequence
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val res = mutableListOf<Vertex?>()
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// Hash set, used to record visited vertices
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val visited = HashSet<Vertex>()
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visited.add(startVet)
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// Queue used to implement BFS
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val que = LinkedList<Vertex>()
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que.offer(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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val vet = que.poll() // Dequeue the vertex at the head of the queue
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res.add(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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que.offer(adjVet) // Only enqueue unvisited vertices
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visited.add(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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/* Driver Code */
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fun main() {
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/* Initialize undirected graph */
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val v = Vertex.valsToVets(intArrayOf(0, 1, 2, 3, 4, 5, 6, 7, 8, 9))
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val edges = arrayOf(
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arrayOf(v[0], v[1]),
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arrayOf(v[0], v[3]),
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arrayOf(v[1], v[2]),
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arrayOf(v[1], v[4]),
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arrayOf(v[2], v[5]),
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arrayOf(v[3], v[4]),
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arrayOf(v[3], v[6]),
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arrayOf(v[4], v[5]),
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arrayOf(v[4], v[7]),
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arrayOf(v[5], v[8]),
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arrayOf(v[6], v[7]),
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arrayOf(v[7], v[8])
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)
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val graph = GraphAdjList(edges)
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println("\nAfter initialization, the graph is")
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graph.print()
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/* Breadth-first traversal */
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val res = graphBFS(graph, v[0]!!)
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println("\nBreadth-first traversal (BFS) vertex sequence is")
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println(Vertex.vetsToVals(res))
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} |