Hi I am trying to find an minimum possible route in my weighted graph using Dijkstra'a algorithm. I am trying to implement the algorithm below from geeksforgeeks.com :
1) Initialize distances of all vertices as infinite.
2) Create an empty priority_queue pq. Every item
of pq is a pair (weight, vertex). Weight (or
distance) is used used as first item of pair
as first item is by default used to compare
two pairs
3) Insert source vertex into pq and make its
distance as 0.
4) While either pq doesn't become empty
a) Extract minimum distance vertex from pq.
Let the extracted vertex be u.
b) Loop through all adjacent of u and do
following for every vertex v.
// If there is a shorter path to v
// through u.
If dist[v] > dist[u] + weight(u, v)
(i) Update distance of v, i.e., do
dist[v] = dist[u] + weight(u, v)
(ii) Insert v into the pq (Even if v is
already there)
5) Print distance array dist[] to print all shortest
paths.
My main Data Structures are:
// HashMap of Intersections
private static HashMap<String, Intersection> intersections;
// Edge/Rail List
private static ArrayList<Rail> railList;
My function below called route and it first gets source and destination vertexes from the commands as String and then i try to implement algorithm above. However i do not know how to store them in final Arraylist so that i can return the path.Additionally, it is problematic i think:
public void route(String wholeLine){
String[] temp = wholeLine.split(" |\\>");
int vel = Integer.parseInt(temp[3]);
double totalpath = 0;
int numOfSwitches = 0;
// My Source and Destination Nodes
Intersection src = intersections.get(temp[1]);
Intersection dest = intersections.get(temp[2]);
// Start the operation
PriorityQueue<Intersection> pq = new PriorityQueue<RailNetwork.Intersection>();
// Setting Distance to 0 for Source Node
src.setDistanceFromSource(0);
pq.add(src);
// While Priority Queue not empty
while(pq.size() != 0){
// Extract the vertex with minimum distance value node from Min Heap. Let the extracted vertex be u.
Intersection u = pq.remove();
// For every adjacent vertex v of u, check if v is in Min Heap.
for(Intersection v : u.getNeigbours()){
double weight = 0;
// Find edgeweight of u and v from rail/edge list
for(int i = 0;i<railList.size();i++){
if(railList.get(i).getSrc().getLabel().equals(u.label) && railList.get(i).getDest().getLabel().equals(v.label)){
weight = railList.get(i).getDistance();
}
else if(railList.get(i).getSrc().getLabel().equals(v.label) && railList.get(i).getDest().getLabel().equals(u.label)){
weight = railList.get(i).getDistance();
}
}
//If v is in Min Heap and distance value is more than weight of u-v plus distance value of u, then update the distance value of v.
if(u.getDistanceFromSource() > v.getDistanceFromSource() + weight){
//Update distance of v, i.e., do dist[v] = dist[u] + weight(u, v)
v.setDistanceFromSource(u.getDistanceFromSource() + weight);
System.out.println(v.label + "\t" + v.distanceFromSource);
pq.add(v);
}
}
}
}
**Could someone please help me to find my mistakes in order to implement it correctly?**Any help or hint is appreciated. Thanks in advance stackoverflow family.
