public void initializePQ(MyGraph graph) {
for (String vertex : graph.getVertices()) {
pq.add(vertex, Double.POSITIVE_INFINITY);
toVisit.add(vertex);
distance.put(vertex, Double.POSITIVE_INFINITY);
parent.put(vertex, null);
}
}
public void executeDijkstra(MyGraph graph, String start) {
initializePQ(graph);
source = start;
pq.changePriority("a", 0.0);
distance.put(source, 0.0);
parent.put(source, source);
visited.add(source);
toVisit.remove(source);
String last_added = pq.removeMin();
HashMap<String, Double> neighbouring_edges = graph.getEdgesFrom(last_added);
while (!toVisit.isEmpty()) {
/*for(String vertex : visited){
System.out.print(vertex + " ");
}
System.out.println();*/
// First change the priorities considering the new crossing edges from last_added.
// last_added is u and vertex is v in the edge (u,v). weight(u,v) is graph.getEdge(u,v)
for (String vertex : neighbouring_edges.keySet()) {
if (toVisit.contains(vertex)) {
if (parent.get(vertex) == null) {
parent.put(vertex, last_added);
distance.put(vertex, distance.get(last_added) + graph.getEdge(last_added, vertex));
pq.changePriority(vertex, distance.get(vertex));
} else {
// if the new crossing edges allow for a shorter path to vertex
if (distance.get(last_added) + graph.getEdge(last_added, vertex)
< distance.get(vertex)) {
parent.put(vertex, last_added);
distance.put(vertex, distance.get(last_added) + graph.getEdge(last_added, vertex));
pq.changePriority(vertex, distance.get(vertex));
}
}
}
}
// Once the pq has been updated, remove the min vertex
last_added = pq.removeMin();
neighbouring_edges = graph.getEdgesFrom(last_added);
toVisit.remove(last_added);
visited.add(last_added);
}
}