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56 lines
2.2 KiB
56 lines
2.2 KiB
/**
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* File: graph_bfs.java
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* Created Time: 2023-02-12
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* Author: krahets (krahets@163.com)
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*/
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package chapter_graph;
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import java.util.*;
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import utils.*;
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public class graph_bfs {
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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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static List<Vertex> graphBFS(GraphAdjList graph, Vertex startVet) {
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// Vertex traversal sequence
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List<Vertex> res = new ArrayList<>();
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// Hash set, used to record visited vertices
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Set<Vertex> visited = new HashSet<>();
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visited.add(startVet);
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// Queue used to implement BFS
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Queue<Vertex> que = new LinkedList<>();
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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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Vertex 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 (Vertex adjVet : graph.adjList.get(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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public static void main(String[] args) {
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/* Initialize undirected graph */
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Vertex[] v = Vertex.valsToVets(new int[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 });
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Vertex[][] edges = { { 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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GraphAdjList graph = new GraphAdjList(edges);
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System.out.println("\nAfter initialization, the graph is");
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graph.print();
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/* Breadth-first traversal */
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List<Vertex> res = graphBFS(graph, v[0]);
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System.out.println("\nBreadth-first traversal (BFS) vertex sequence is");
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System.out.println(Vertex.vetsToVals(res));
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}
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}
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