public static void main(String[] args) throws Exception {
int V, E, s, a, b, w;
File f = new File("in_06.txt");
Scanner sc = new Scanner(f);
V = sc.nextInt();
E = sc.nextInt();
s = sc.nextInt();
AdjList.clear();
for (int i = 0; i < V; i++) {
Vector<IntegerPair> Neighbor = new Vector<IntegerPair>();
AdjList.add(Neighbor); // add neighbor list to Adjacency List
}
for (int i = 0; i < E; i++) {
a = sc.nextInt();
b = sc.nextInt();
w = sc.nextInt();
AdjList.get(a).add(new IntegerPair(b, w)); // first time using weight
}
// as an example, we start from this source (see Figure 1.15)
Vector<Integer> dist = new Vector<Integer>();
dist.addAll(Collections.nCopies(V, INF));
dist.set(s, 0);
// Bellman Ford routine
for (int i = 0; i < V - 1; i++) // relax all E edges V-1 times, O(V)
for (int u = 0; u < V; u++) { // these two loops = O(E)
Iterator it = AdjList.get(u).iterator();
while (it.hasNext()) { // relax these edges
IntegerPair v = (IntegerPair) it.next();
dist.set(v.first(), Math.min(dist.get(v.first()), dist.get(u) + v.second()));
}
}
boolean negative_cycle_exist = false;
for (int u = 0; u < V; u++) { // one more pass to check
Iterator it = AdjList.get(u).iterator();
while (it.hasNext()) { // relax these edges
IntegerPair v = (IntegerPair) it.next();
if (dist.get(v.first()) > dist.get(u) + v.second()) // should be false, but if possible
negative_cycle_exist = true; // then negative cycle exists!
}
}
System.out.printf("Negative Cycle Exist? %s\n", negative_cycle_exist ? "Yes" : "No");
if (!negative_cycle_exist)
for (int i = 0; i < V; i++) System.out.printf("SSSP(%d, %d) = %d\n", s, i, dist.get(i));
}
// You can add extra function if needed
// --------------------------------------------
int dijkstra() {
IntegerPair current;
while (!q.isEmpty()) {
current = q.poll();
if (weights.get(current.first()) == current.second())
for (IntegerPair next : AdjList.get(current.first())) {
if (weights.get(next.first()) > current.second() + next.second()) {
weights.set(next.first(), current.second() + next.second());
q.offer(new IntegerPair(next.first(), weights.get(next.first())));
}
}
}
return weights.get(1);
}
