Exemple #1
0
  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));
  }
Exemple #2
0
  // 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);
  }