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hello-algo/codes/java/chapter_graph/graph_adjacency_list.java

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/**
* File: graph_adjacency_list.java
* Created Time: 2023-01-26
* Author: krahets (krahets@163.com)
*/
package chapter_graph;
import java.util.*;
import utils.*;
/* 基于邻接表实现的无向图类 */
class GraphAdjList {
// 邻接表key顶点value该顶点的所有邻接顶点
Map<Vertex, List<Vertex>> adjList;
/* 构造方法 */
public GraphAdjList(Vertex[][] edges) {
this.adjList = new HashMap<>();
// 添加所有顶点和边
for (Vertex[] edge : edges) {
addVertex(edge[0]);
addVertex(edge[1]);
addEdge(edge[0], edge[1]);
}
}
/* 获取顶点数量 */
public int size() {
return adjList.size();
}
/* 添加边 */
public void addEdge(Vertex vet1, Vertex vet2) {
if (!adjList.containsKey(vet1) || !adjList.containsKey(vet2) || vet1 == vet2)
throw new IllegalArgumentException();
// 添加边 vet1 - vet2
adjList.get(vet1).add(vet2);
adjList.get(vet2).add(vet1);
}
/* 删除边 */
public void removeEdge(Vertex vet1, Vertex vet2) {
if (!adjList.containsKey(vet1) || !adjList.containsKey(vet2) || vet1 == vet2)
throw new IllegalArgumentException();
// 删除边 vet1 - vet2
adjList.get(vet1).remove(vet2);
adjList.get(vet2).remove(vet1);
}
/* 添加顶点 */
public void addVertex(Vertex vet) {
if (adjList.containsKey(vet))
return;
// 在邻接表中添加一个新链表
adjList.put(vet, new ArrayList<>());
}
/* 删除顶点 */
public void removeVertex(Vertex vet) {
if (!adjList.containsKey(vet))
throw new IllegalArgumentException();
// 在邻接表中删除顶点 vet 对应的链表
adjList.remove(vet);
// 遍历其他顶点的链表,删除所有包含 vet 的边
for (List<Vertex> list : adjList.values()) {
list.remove(vet);
}
}
/* 打印邻接表 */
public void print() {
System.out.println("邻接表 =");
for (Map.Entry<Vertex, List<Vertex>> pair : adjList.entrySet()) {
List<Integer> tmp = new ArrayList<>();
for (Vertex vertex : pair.getValue())
tmp.add(vertex.val);
System.out.println(pair.getKey().val + ": " + tmp + ",");
}
}
}
public class graph_adjacency_list {
public static void main(String[] args) {
/* 初始化无向图 */
Vertex[] v = Vertex.valsToVets(new int[] { 1, 3, 2, 5, 4 });
Vertex[][] edges = { { v[0], v[1] }, { v[0], v[3] }, { v[1], v[2] },
{ v[2], v[3] }, { v[2], v[4] }, { v[3], v[4] } };
GraphAdjList graph = new GraphAdjList(edges);
System.out.println("\n初始化后图为");
graph.print();
/* 添加边 */
// 顶点 1, 2 即 v[0], v[2]
graph.addEdge(v[0], v[2]);
System.out.println("\n添加边 1-2 后,图为");
graph.print();
/* 删除边 */
// 顶点 1, 3 即 v[0], v[1]
graph.removeEdge(v[0], v[1]);
System.out.println("\n删除边 1-3 后,图为");
graph.print();
/* 添加顶点 */
Vertex v5 = new Vertex(6);
graph.addVertex(v5);
System.out.println("\n添加顶点 6 后,图为");
graph.print();
/* 删除顶点 */
// 顶点 3 即 v[1]
graph.removeVertex(v[1]);
System.out.println("\n删除顶点 3 后,图为");
graph.print();
}
}