JAVA實現圖的鄰接表以及DFS

一：定義鄰接表結構儲存圖

package 圖的遍歷;

//鄰接表實現圖的建立

//儲存邊
class EdgeNode {
	int index; // 習慣了用index，其實標准寫法是(adjVertex)
	int value; // 權值
	EdgeNode nextArc; // 指向下一條弧
}

// 鄰接表節點的類型
class VertexNode {
	String name;
	EdgeNode firstArc = new EdgeNode(); // 指向第一條弧
}

public class Graph {
	VertexNode[] adjList; // 保存鄰接表的頭節點
	int e; // 圖的邊數
	int v; // 圖的頂點數
	boolean[] visit;

	public Graph(int v, int e) {
		this.v = v;
		this.e = e;
		adjList = new VertexNode[e + 1]; // 學習Java養成的好習慣，動態分配空間,創建頂點表數組
		visit = new boolean[e + 1];  //標記
		for (int i = 0; i < e; i++) {
			visit[i] = false;
		}
	}
}

　　二：DFS過程

package 圖的遍歷;

public class DFSGraph {
	public static void DFS(Graph G, int k) {
		System.out.println(G.adjList[k].name);
		G.visit[k] = true;
		EdgeNode p = new EdgeNode();
		p = G.adjList[k].firstArc;
		while(p!=null){
			if(G.visit[p.index]!=true){
				DFS(G,p.index);
			}
			  
			p=p.nextArc;
		}
	}

}

　　三：建立圖

package 圖的遍歷;

import java.util.Scanner;

public class CreateGraph {
	private static Graph G;
	public static Graph getGraph(){
		return G;
	}
	public static void createGraph() {
		Scanner sc = new Scanner(System.in);
		System.out.println("請輸入頂點數v和邊數e:");
		int v = sc.nextInt();
		int e = sc.nextInt();
		G = new Graph(v, e);
		System.out.println("請輸入各頂點信息:");
		for (int i = 0; i < G.v; i++) {
			G.adjList[i] = new VertexNode();
			G.adjList[i].name = sc.next();
			G.adjList[i].firstArc = null; // 不可或缺
		}
		System.out.println("請輸入各邊信息(用空格隔開):");
		for (int i = 0; i < G.e; i++) {
			EdgeNode en1 = new EdgeNode();
			// 保證e1,e2都是合法輸入
			String e1 = sc.next();
			String e2 = sc.next();
			int v1 = Index(e1);
			int v2 = Index(e2);
			en1.index = v1; // en1的下標是v1
			en1.nextArc = G.adjList[v2].firstArc;
			G.adjList[v2].firstArc = en1;
			
			EdgeNode en2 = new EdgeNode();
			en2.index = v2; // en2的下標是v2
			en2.nextArc = G.adjList[v1].firstArc;
			G.adjList[v1].firstArc = en2;
		}
	}
	public static void outputGraph() {  //不知道為何空指針異常
		try {
			System.out.println("輸出鄰接表存儲情況：");
			EdgeNode en = new EdgeNode();
			for (int i = 0; i < G.e; i++) {
				System.out.print(G.adjList[i].name);
				en = G.adjList[i].firstArc;
				while (en != null) {
					System.out.print("->" + G.adjList[en.index].name);
					en = en.nextArc;
				}
				System.out.println();
			}
		} catch (NullPointerException e) {

		}

	}
	private static int Index(String e1) {
		for (int i = 0; i < G.v; i++) {
			if (G.adjList[i].name.equals(e1)){
				return i;
			}
		}
		return -1;
	}
}

　　四：測試

package 圖的遍歷;


public class GraphDemo {
	public static void main(String[] args) {
		CreateGraph.createGraph();
		CreateGraph.outputGraph();
		
		System.out.println("DFS圖的過程如下：");
		DFSGraph.DFS(CreateGraph.getGraph() , 0);
	}
}
/*
 * 請輸入頂點數v和邊數e: 4 5 
 * 請輸入各頂點信息: a b c d 
 * 請輸入各邊信息(用空格隔開): 
 * a b
 * a c
 * a d 
 * b c 
 * b d
 */

　　五，測試結果