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/**
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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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/* 广度优先遍历 */
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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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fun graphBFS(graph: GraphAdjList, startVet: Vertex): List<Vertex> {
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// 顶点遍历序列
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val res: MutableList<Vertex> = ArrayList()
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// 哈希表，用于记录已被访问过的顶点
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val visited: MutableSet<Vertex> = HashSet()
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visited.add(startVet)
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// 队列用于实现 BFS
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val que: Queue<Vertex> = LinkedList()
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que.offer(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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val vet = que.poll() // 队首顶点出队
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res.add(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)) continue // 跳过已被访问的顶点
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que.offer(adjVet) // 只入队未访问的顶点
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visited.add(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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/* Driver Code */
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fun main() {
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/* 初始化无向图 */
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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("\n初始化后，图为")
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graph.print()
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/* 广度优先遍历 */
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val res = graphBFS(graph, v[0]!!)
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println("\n广度优先遍历（BFS）顶点序列为")
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println(Vertex.vetsToVals(res))
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}
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