Hi, I have difficulty understanding these code.
import java.util.PriorityQueue;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
class Vertex implements Comparable<Vertex> {
public final String name;
public Edge[] adjacencies;
public double minDistance = Double.POSITIVE_INFINITY;
public Vertex previous;
public Vertex(String argName) {
name = argName;
}
public String toString() {
return name;
}
public int compareTo(Vertex other) {
return Double.compare(minDistance, other.minDistance);
}
}
class Edge {
public final Vertex target;
public final double weight;
public Edge(Vertex argTarget, double argWeight) {
target = argTarget;
weight = argWeight;
}
}
public class Dijkstra {
public static void computePaths(Vertex source) {
source.minDistance = 0.;
PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
vertexQueue.add(source);
while (!vertexQueue.isEmpty()) {
Vertex u = vertexQueue.poll();
for (Edge e : u.adjacencies) {
Vertex v = e.target;
double weight = e.weight;
double distanceThroughU = u.minDistance + weight;
if (distanceThroughU < v.minDistance) {
vertexQueue.remove(v);
v.minDistance = distanceThroughU;
v.previous = u;
vertexQueue.add(v);
}
}
}
}
public static List<Vertex> getShortestPathTo(Vertex target) {
List<Vertex> path = new ArrayList<Vertex>();
for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
path.add(vertex);
Collections.reverse(path);
return path;
}
public static void main(String[] args) {
Vertex v0 = new Vertex("Harrisburg");
Vertex v1 = new Vertex("Baltimore");
Vertex v2 = new Vertex("Washington");
Vertex v3 = new Vertex("Philadelphia");
Vertex v4 = new Vertex("Binghamton");
Vertex v5 = new Vertex("Allentown");
Vertex v6 = new Vertex("New York");
v0.adjacencies = new Edge[] { new Edge(v1, 79.83), new Edge(v5, 81.15) };
v1.adjacencies = new Edge[] { new Edge(v0, 79.75), new Edge(v2, 39.42),
new Edge(v3, 103.00) };
v2.adjacencies = new Edge[] { new Edge(v1, 38.65) };
v3.adjacencies = new Edge[] { new Edge(v1, 102.53),
new Edge(v5, 61.44), new Edge(v6, 96.79) };
v4.adjacencies = new Edge[] { new Edge(v5, 133.04) };
v5.adjacencies = new Edge[] { new Edge(v0, 81.77), new Edge(v3, 62.05),
new Edge(v4, 134.47), new Edge(v6, 91.63) };
v6.adjacencies = new Edge[] { new Edge(v3, 97.24), new Edge(v5, 87.94) };
Vertex[] vertices = { v0, v1, v2, v3, v4, v5, v6 };
computePaths(v0);
for (Vertex v : vertices) {
System.out.println("Distance to " + v + ": " + v.minDistance);
List<Vertex> path = getShortestPathTo(v);
System.out.println("Path: " + path);
}
}
}
The part in the main method computePaths(v0);
v0 is the source, and if i want to continue and find v1's shortest path to all destination, what i have done is by copying the same for loop and change the source to "v1".
This is what i have done, but it does not work as it is still obtaining the v0's shortest path.
computePaths(v1);
for (Vertex v : vertices) {
System.out.println("Distance to " + v + ": " + v.minDistance);
List<Vertex> path = getShortestPathTo(v);
System.out.println("Path: " + path);
Any kind souls able to help me fix this issue?