private void relaxD(Route r, int v) {
// relax edge e and update pq if changed
City city2 = r.other(cities[v]);
int w = city2.id() - 1;
if (distTo[w] > distTo[v] + r.distance()) {
distTo[w] = distTo[v] + r.distance();
edgeTo[w] = r;
if (pq.contains(w)) pq.change(w, distTo[w]);
else pq.insert(w, distTo[w]);
}
}
private void scan(int v) {
marked[v] = true;
for (Route r : adj[v]) {
int w = r.other(cities[v]).id() - 1; // index of other city in route
if (marked[w]) {
continue; // v-w is obsolete edge
}
if (r.distance() < distTo[w]) {
distTo[w] = r.distance();
edgeTo[w] = r;
if (pq.contains(w)) {
pq.change(w, distTo[w]);
} else {
pq.insert(w, distTo[w]);
}
}
}
}
private void prim(int s, StringBuilder sb) {
distTo[s] = 0;
pq.insert(s, distTo[s]);
while (!pq.isEmpty()) {
int v = pq.delMin();
if (v != s) {
Route r = edgeTo[v];
String str = String.format("%s, %s : %d\n", r.fst(), r.snd(), r.distance());
sb.append(str);
}
scan(v);
}
}
// Option 3
public void shortestByDistance(String c1, String c2) {
System.out.println("SHORTEST DISTANCE PATH from " + c1 + " to " + c2);
System.out.println("--------------------------------------------------------");
City city1 = null;
City city2 = null;
for (int i = 0; i < numCities; i++) {
if (cities[i].name().equals(c1)) {
city1 = cities[i];
}
if (cities[i].name().equals(c2)) {
city2 = cities[i];
}
}
if (c1.equals(c2) || city1 == null || city2 == null) {
System.out.println("Invalid city choice(s)");
return;
}
distTo = new int[numCities];
edgeTo = new Route[numCities];
for (int i = 0; i < numCities; i++) distTo[i] = Integer.MAX_VALUE;
distTo[city1.id() - 1] = 0;
// relax vertices in order of distance from s
pq = new IndexMinPQ<Integer>(numCities);
pq.insert(city1.id() - 1, distTo[city1.id() - 1]);
while (!pq.isEmpty()) {
int v = pq.delMin();
for (Route r : adj[v]) relaxD(r, v);
}
if (distTo[city2.id() - 1] == Integer.MAX_VALUE) {
System.out.println("No path");
return;
}
System.out.printf("Shortest distance from %s to %s is %d\n", c1, c2, distTo[city2.id() - 1]);
System.out.println("Path with edges (in reverse order):");
City currCity = city2;
for (Route r = edgeTo[city2.id() - 1]; r != null; r = edgeTo[currCity.id() - 1]) {
System.out.print(currCity + " " + r.distance() + " ");
currCity = r.other(currCity);
}
System.out.println(currCity);
}