Dijkstra最短路径算法

标签：dijkstra   算法   

import java.util.ArrayList;

/**
 * @ClassName:   Graph
 * @Description: 基于Dijkstra算法的最短路径求解
 * @author       zhoupengcheng
 * @version      2015年4月29日上午9:37:43
 */

public class Graph {
	private final int MAX_NUM = 20000;
	private final int INFINITY = 100000;
	private ArrayList<Vertex> vertexList;// ArrayList保存所有结点
	private int adjMatrix[][];//邻接矩阵
	private int nVerts;// 保存当前图中当前顶点数
	private int nTree; // 保存已经加入到最短路径上的结点
	//private DistPar sPath[];//保存源点到每个点的当前最短路径距离
	private ArrayList<DistPar> sPath;
	private int currentVert;//搜索最短路径到达的当前结点
	private int startToCurrent;//源点到当前结点的(最短)距离
	//--------------------构造函数--------------------
	public Graph(){
		vertexList=new ArrayList<Vertex>();
		adjMatrix=new int[MAX_NUM][MAX_NUM];
		nVerts=0;
		nTree=0;
		for(int i=0;i<MAX_NUM;i++){
			for(int j=0;j<MAX_NUM;j++)
				adjMatrix[i][j]=INFINITY;
		}
		//sPath=new DistPar[MAX_NUM];
		sPath=new ArrayList<DistPar>();
	}
	
	//---------------------------------------------
	public void addVertex(String lab,int id){
		vertexList.add(new Vertex(lab,id));
		nVerts++;
	}
	//---------------------------------------------
	public void addEdge(int start, int end,int weight) {
		adjMatrix[start][end] = weight;//有向带权图
	}
	//---------------------------------------------
	public void path(int startTree){//寻找最短路径
		//int startTree=0;//假设都是从下标为0的点开始搜索
		vertexList.get(startTree).isIntree=true;
		nTree=1;
		
		//根据邻接矩阵中两点的权值构造初始的sPath,sPath在搜索最短路径的过程中不断更新
		for(int k=0;k<nVerts;k++){
			int tmpDist=adjMatrix[startTree][k];
			//sPath[k]=new DistPar(startTree,tmpDist);
			sPath.add(new DistPar(startTree,tmpDist));
		}
		
		//直到所有的结点都已经加入到最短路径中,否则继续迭代
		while(nTree<nVerts){
			int indexMin=getMin();//从sPath中获取最小的路径
			//int minDist=sPath[indexMin].distance;
			int minDist=sPath.get(indexMin).distance;
			if(minDist==INFINITY){
				System.out.println("无法到达未连通的结点!");
				break;
			}else{
				currentVert=indexMin;
				//startToCurrent=sPath[indexMin].distance;
				startToCurrent=sPath.get(indexMin).distance;
			}
			vertexList.get(currentVert).isIntree=true;
			nTree++;
			adjust_sPath();
		}
		
		displayPaths(startTree);//打印最短路径搜索结果
		nTree=0;
		//清空标志位,还原一个没有遍历过的树
		for(int j=0;j<nVerts;j++){
			vertexList.get(j).isIntree=false;
		}
	}
	//------------从sPath中获得一个离源点距离最短的结点----------
	private int getMin() {
		// TODO Auto-generated method stub
		int minDist=INFINITY;
		int indexMin=0;
		for(int j=0;j<nVerts;j++){
			if(!vertexList.get(j).isIntree&&sPath.get(j).distance<minDist){
				indexMin=j;
				minDist=sPath.get(j).distance;
			}
		}
		return indexMin;
	}
	//------------调整sPath中的值,更新最新的最短距离(距源点)------------
	private void adjust_sPath() {
		// TODO Auto-generated method stub
		int column=0;//起始点就不要更新了
		while(column<nVerts){
			if(vertexList.get(column).isIntree)
			{
				column++;
				continue;
			}
			
			int currentToFringe=adjMatrix[currentVert][column];
			int startToToFringe=currentToFringe+startToCurrent;
			int sPathDist=sPath.get(column).distance;
			if(startToToFringe<sPathDist){
				sPath.get(column).distance=startToToFringe;
				sPath.get(column).parentVert=currentVert;
			}
			column++;
		}
	}

	private void displayPaths(int srcVertex) {
		// TODO Auto-generated method stub
		for(int i=0;i<nVerts;i++){
			System.out.print(vertexList.get(i).label+"=");
			if(sPath.get(i).distance==INFINITY){
				System.out.print("inf");
			}else{
				System.out.print(sPath.get(i).distance);
			}
			String parent=vertexList.get(sPath.get(i).parentVert).label;
			System.out.print("("+parent+") ");
		}
		System.out.println();
		// 打印源点到图中每个点走过的最短路径,根据DistPar对象的parent结点来找路径
		for (int j = 0; j < nVerts; j++) {
			if (sPath.get(j).distance == INFINITY)
				continue;
			if (j == srcVertex)
				continue;
			int x = sPath.get(j).parentVert;
			if (x == srcVertex) {
				System.out.print(vertexList.get(j).label + "<-"
						+ vertexList.get(srcVertex).label + " ");
			} else {
				System.out.print(vertexList.get(j).label + "<-");
				while (x != srcVertex) {
					System.out.print(vertexList.get(x).label + "<-");
					x = sPath.get(x).parentVert;
				}
				System.out.print(vertexList.get(srcVertex).label);
			}
			System.out.println("");
		}
	}
	
}

 

/**
 * @ClassName:   Main
 * @Description: 工程的main函数
 * @author       zhoupengcheng
 * @version      2015年4月29日上午9:39:12
 */
public class Main {
	public static void main(String[] args) {
		Graph theGraph = new Graph();
		int num = 0;
		theGraph.addVertex("A", num++); // 0 (start)
		theGraph.addVertex("B", num++); // 1
		theGraph.addVertex("C", num++); // 2
		theGraph.addVertex("D", num++); // 3
		theGraph.addVertex("E", num++); // 4
		//theGraph.addVertex("F", num++); // 5
		
		theGraph.addEdge(0, 1, 50); // AB 50
		theGraph.addEdge(0, 3, 80); // AD 80
		theGraph.addEdge(1, 2, 60); // BC 60
		theGraph.addEdge(1, 3, 90); // BD 90
		theGraph.addEdge(2, 4, 40); // CE 40
		theGraph.addEdge(3, 2, 20); // DC 20
		theGraph.addEdge(3, 4, 70); // DE 70
		theGraph.addEdge(4, 1, 50); // EB 50

		//构造无向图
//		theGraph.addEdge(1, 0, 50); // AB 50
//		theGraph.addEdge(3, 0, 80); // AD 80
//		theGraph.addEdge(2, 1, 60); // BC 60
//		theGraph.addEdge(3, 1, 90); // BD 90
//		theGraph.addEdge(4, 2, 40); // CE 40
//		theGraph.addEdge(2, 3, 20); // DC 20
//		theGraph.addEdge(4, 3, 70); // DE 70
//		theGraph.addEdge(1, 4, 50); // EB 50
		
		System.out.println("Shortest paths");
		theGraph.path(0); // 设置源点
		System.out.println();
	}
}

/**
 * @ClassName:   DistPar
 * @Description: 此类的实例是存放在sPath数组中的
 * @author       zhoupengcheng
 * @version      2015年4月29日上午9:40:38
 */
public class DistPar {
	public int distance;// 保存源点(起点)到此结点的当前最短距离
	public int parentVert;// 在最短路径中此结点的上一个(父)结点,设置此属性是为了方便输出路径序列

	public DistPar(int parent,int distance) {
		// TODO Auto-generated constructor stub
		this.parentVert=parent;
		this.distance=distance;
	}
}

/**
 * @ClassName:   Vertex
 * @Description: 结点类
 * @author       zhoupengcheng
 * @version      2015年4月29日上午9:41:03
 */
public class Vertex {
	public String label;//节点的内容,一个元组的数据摘要
	public boolean isIntree;//标记该点是否已经包含在最短路径中
	public int id;//标识这个数据结点,到时要输出包含关键词节点的ID另作处理
	
	public Vertex(String label,int id){
		this.label=label;
		this.id=id;
		this.isIntree=false;
	}
}

Dijkstra最短路径算法

标签：dijkstra   算法   

原文地址：http://blog.csdn.net/hellozpc/article/details/45439555