Dijkstra最短路徑演算法的java實現__演算法

package graph;import java.util.HashMap;import java.util.Iterator;import java.util.LinkedList;import java.util.Map;import java.util.Map.Entry;/** * @author wyhong * */public class Dijkstra {public class Node{/** * 節點的標識符 */private Integer identifier;/** * 該節點是否被訪問過 */private boolean visited = false;/** * 該節點與其他節點的映射關係 */private Map<Node,Integer> mapping = new HashMap<Node,Integer>();public Integer getIdentifier() {return identifier;}public void setIdentifier(Integer identifier) {this.identifier = identifier;}public boolean isVisited() {return visited;}public void setVisited(boolean visited) {this.visited = visited;}public Map<Node, Integer> getMapping() {return mapping;}}/** * Getting optimal path by Dijkstra algorithm * @param src * @param dest * @return */public static LinkedList<Node> getOptimalPath(Node src, Node dest){return dijkstra(src, dest, 0, 0, new LinkedList<Node>());}/** * Dijkstra algorithm * @param src 起始節點 * @param dest 目標節點 * @param adjacentDist 起始節點與目標節點相鄰時的距離 * @param optimalDist 最短路徑權值之和 * @param optimalPath 最短路徑 * @return */private static LinkedList<Node> dijkstra(Node src, Node dest, int adjacentDist, int optimalDist, LinkedList<Node> optimalPath){if(optimalPath.size()==0){optimalPath.add(src);}//當前節點與其他節點的映射關係Map<Node,Integer> mapping = src.getMapping();//當前節點與其相鄰節點的最小距離int partialMinDist = 0;//當前預選的下一最優節點Node partialOptimalNode = null;Iterator<Entry<Node, Integer>> entryIterator = mapping.entrySet().iterator();while (entryIterator.hasNext()) {Entry<Node, Integer> entry = (Entry<Node, Integer>) entryIterator.next();Node nextNode = entry.getKey();//判斷該相鄰節點是否被訪問過if (nextNode.isVisited()) continue;int dist = entry.getValue(); //終點與起點相鄰，但未必路徑最短if(nextNode.getIdentifier() == dest.getIdentifier() && optimalPath.size() == 1) adjacentDist = dist;if (partialMinDist != 0) {boolean currentIsOptimal = partialMinDist > dist ? false : true;if(!currentIsOptimal){partialMinDist = dist;partialOptimalNode = nextNode;}}else{partialMinDist = dist;partialOptimalNode = nextNode;}}//設定當前節點已被訪問src.setVisited(true);//加入鏈表optimalPath.add(partialOptimalNode);optimalDist += partialMinDist;if(partialOptimalNode.getIdentifier()!=dest.getIdentifier()){//若未到終點時當前最優路徑長度已大於終點與起點相鄰的距離，則最短路徑為起點--->終點if(adjacentDist != 0 && optimalDist > adjacentDist) {src = optimalPath.removeFirst();optimalPath.clear();optimalPath.add(src);optimalPath.add(dest);optimalDist = adjacentDist;return optimalPath;}//否則以當前節點遞迴return dijkstra(partialOptimalNode, dest, adjacentDist, optimalDist, optimalPath);}else{return optimalPath;}}}

測試案例：

package graph.test;import graph.Dijkstra;import graph.Dijkstra.Node;import java.util.Iterator;import java.util.LinkedList;public class DijkstraTest {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubDijkstra dijkstra = new Dijkstra();Dijkstra.Node node_1 = dijkstra.new Node();Dijkstra.Node node_2 = dijkstra.new Node();Dijkstra.Node node_3 = dijkstra.new Node();Dijkstra.Node node_4 = dijkstra.new Node();Dijkstra.Node node_5 = dijkstra.new Node();Dijkstra.Node node_6 = dijkstra.new Node();node_1.setIdentifier(1);node_1.getMapping().put(node_2, 7);node_1.getMapping().put(node_3, 9);node_1.getMapping().put(node_6, 14);node_2.setIdentifier(2);node_2.getMapping().put(node_1, 7);node_2.getMapping().put(node_3, 10);node_2.getMapping().put(node_4, 15);node_3.setIdentifier(3);node_3.getMapping().put(node_1,7);node_3.getMapping().put(node_2,10);node_3.getMapping().put(node_4,11);node_3.getMapping().put(node_6,2);node_4.setIdentifier(4);node_4.getMapping().put(node_3, 11);node_4.getMapping().put(node_2, 15);node_4.getMapping().put(node_5, 6);node_5.setIdentifier(5);node_5.getMapping().put(node_4, 6);node_5.getMapping().put(node_6, 9);node_6.setIdentifier(6);node_6.getMapping().put(node_5, 9);node_6.getMapping().put(node_1, 14);LinkedList<Node> optimalPath = Dijkstra.getOptimalPath(node_1, node_5);System.out.println("-------The optimal path--------");for (Iterator<Node> iterator = optimalPath.iterator(); iterator.hasNext();) {Node node = (Node) iterator.next();if (iterator.hasNext()) {System.out.print(node.getIdentifier()+"-->");}else{System.out.print(node.getIdentifier());}}}}

結果：