java - 打印前人的 Dijkstra 算法

Question

我正在尝试打印 Dijkstra 算法，但目前仅从我的 getPath() 方法打印目标 ID。我的想法是从目标顶点向后工作并打印每个前导顶点，直到打印起始顶点。如果有另一种方法来存储/打印路径，我将非常愿意尝试不同的方式，我很欣赏任何想法!

class ShortestPathFinder {
        private  Graph graph = new Graph();
        private  Vertex source = new Vertex(0, null);
        private Vertex destination = new Vertex(0,null);

        private  Map<Vertex,Vertex> previousVertex = new HashMap();
        private  Set<Vertex> visited =  new HashSet();

    public Optional<Path> findShortestPath(Graph graph, Vertex source, Vertex destination, ReadInput graphReader) {

        this.destination = destination;
        this.source = source;
        Optional<Path> pathFound = Optional.empty();
        source.setDistanceFromSource(0);
        PriorityQueue<Vertex> priorityQueue = new PriorityQueue<>();
        priorityQueue.add(source);
        source.setVisited(true);
        boolean destinationFound = false;

        while( !priorityQueue.isEmpty() && destinationFound == false){
            // Getting the minimum distance vertex from priority queue
            Vertex actualVertex = priorityQueue.poll();
            System.out.println("working on: " + actualVertex.getID());

            actualVertex = graphReader.SetAdjList(actualVertex);

            for(Edge edge : actualVertex.getAdjacenciesList()){
                Vertex v = edge.getTargetVertex();
                System.out.println("a Neighbor is: " + v.getID());
                if(!v.isVisited()) {
                    if(v.getID() == destination.getID()) {
                        System.out.println("Destination found");
                        Path path = new Path(previousVertex);
                        pathFound = Optional.of(path);
                        destinationFound = true;
                        break;
                    }
                    double newDistance = actualVertex.getDistanceFromSource() + edge.getWeight();

                    if( newDistance < v.getDistanceFromSource() ){
                        priorityQueue.remove(v);
                        v.setDistanceFromSource(newDistance);
                        v.setPredecessor(actualVertex);
                        priorityQueue.add(v);
                        System.out.println("Added: " + v.getID());
                    }
                }
            }
            actualVertex.setVisited(true);
        }   
        return pathFound;       
    }

    public List<Vertex> getPath() {
        List<Vertex> path = new ArrayList<>();

        for(Vertex vertex=destination;vertex!=null;vertex=vertex.getPredecessor()){
            path.add(vertex);
        }
        Collections.reverse(path);
        return path;

    }       
}

Answer 1

到达目的地时，将调用代码中的以下部分:

                    if(v.getID() == destination.getID()) {
                        System.out.println("Destination found");
                        Path path = new Path(previousVertex);
                        pathFound = Optional.of(path);
                        destinationFound = true;
                        break;
                    }

相应的 v 从未设置过其前任，这是您的 getPath() 方法所依赖的。考虑在 if 语句中设置它，如下所示:

                    if(v.getID() == destination.getID()) {
                        System.out.println("Destination found");
                        destination.setPredecessor(actualVertex); // sets the predecessor for backwards traversal
                        Path path = new Path(previousVertex);
                        pathFound = Optional.of(path);
                        destinationFound = true;
                        break;
                    }