Dijkstra无向图的最短路径

Question

My following code is working perfectly fine for directed graphs and when given an undirected graph, it will not return the shortest path.

public void Djikstra(int s){
    boolean[] marked = new boolean[V];
    dist = new double[V];

    for(int i = 0; i<V; i++){ # initializing array
        dist[i] = Double.POSITIVE_INFINITY;
    }
    dist[s] = 0.0;

    Queue<Integer> pqs = new PriorityQueue<Integer>();

    pqs.add(s);
    while(!pqs.isEmpty()){
        int v = pqs.poll();

        if(marked[v]) continue;
        marked[v] = true;

        for(Edge e : get_list(v)){ # get_list(v) will return an iterable from the adjacency list at index v 
            v = e.getV()
            int w = e.getW();
            if(dist[w] > dist[v] + e.getWeight()){
                dist[w] = dist[v] + e.getWeight();
                distances[w] = e #all the distances will be stored in this array
                pqs.add(w);
            }
        }
    }
}

I'm not sure what's my mistake over here? I'm kind of sure it's a simple error, some hints will do the job.

Thanks.

Edit:

public void addEdge(Edge e){
    adj[e.getV()].add(e);
    adj[e.getW()].add(e);
}

Answer 1

Consider the differences between a directed path from node 1 to 2 and an undirected path from node 1 to 2.

What would you need to add to the directed graph (which your algorithm can solve) to make it equivalent to the undirected graph?

EDIT:

Figured it out, I think. Here's the hint: You are currently changing resetting v inside of your for loop. This will not cause an error with a directed graph, but what happens if the edge is listed as going from w to v instead of v to w undirected?

EDIT2:

Something like this:

First, remove v = e.getV();

Second, change the next line to int w = (v == e.getV()) ? e.getW() : e.getV(); int w = (v == e.getV()) ? e.getW() : e.getV();

This sets the value of w to whichever vertex of your edge v is NOT.

This second suggestion is equivalent to the following (maybe a bit easier to read):

int w = e.getW();
if (w == v) {
    w = e.getV();
}

Answer 2

You have to add two different edges, the direct and the inverse. Change

public void addEdge(Edge e){
    adj[e.getV()].add(e);
    adj[e.getW()].add(e);
}

in

public void addEdge(Edge e){
    adj[e.getV()].add(e);
}

and, when you add the edges, do it like this:

Edge e = new Edge(from, to, weight);
Edge f = new Edge(to, from, weight);

addEdge(e);
addEdge(f);