package algs42;
import stdlib.*;
import algs13.Queue;
/* ***********************************************************************
 *  Compilation:  javac BruteSCC.java
 *  Dependencies: Digraph.java TransitiveClosure.java
 *
 *  Compute the strongly-connected components of a digraph using
 *  brute force.
 *
 *  Runs in O(EV) time.
 *
 *  % java BruteSCC tinyDG.txt
 *  5 components
 *  0 2 3 4 5
 *  1
 *  6
 *  7 8
 *  9 10 11 12
 *
 *************************************************************************/

public class XBruteSCC {
  private int count;    // number of strongly connected components
  private final int[] id;     // id[v] = id of strong component containing v

  public XBruteSCC(Digraph G) {

    // initially each vertex is in its own component
    id = new int[G.V()];
    for (int v = 0; v < G.V(); v++)
      id[v] = v;

    // compute transitive closure
    TransitiveClosure tc = new TransitiveClosure(G);

    // if v and w are mutally reachable, assign v to w's component
    for (int v = 0; v < G.V(); v++)
      for (int w = 0; w < v; w++)
        if (tc.reachable(v, w) && tc.reachable(w, v))
          id[v] = id[w];

    // compute number of strongly connected components
    for (int v = 0; v < G.V(); v++)
      if (id[v] == v)
        count++;
  }

  // return the number of strongly connected components
  public int count() { return count; }

  // are v and w strongly connected?
  public boolean stronglyConnected(int v, int w) {
    return id[v] == id[w];
  }

  // in which strongly connected component is vertex v?
  public int id(int v) { return id[v]; }


  public static void main(String[] args) {
    args = new String[] { "data/tinyDG.txt" };

    In in = new In(args[0]);
    Digraph G = DigraphGenerator.fromIn(in);
    XBruteSCC scc = new XBruteSCC(G);

    // number of connected components
    int M = scc.count();
    StdOut.println(M + " components");

    // compute list of vertices in each strong component
    @SuppressWarnings("unchecked")
    final
    Queue<Integer>[] components = new Queue[G.V()];
    for (int i = 0; i < G.V(); i++) {
      components[i] = new Queue<>();
    }
    for (int v = 0; v < G.V(); v++) {
      components[scc.id(v)].enqueue(v);
    }

    // print results
    for (int i = 0; i < G.V(); i++) {
      if (!components[i].isEmpty()) {
        for (int v : components[i]) {
          StdOut.print(v + " ");
        }
        StdOut.println();
      }
    }

  }

}