package algs42;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac TransitiveClosure.java
 *  Execution:    java TransitiveClosure filename.txt
 *  Dependencies: Digraph.java DepthFirstDirectedPaths.java In.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/42directed/tinyDG.txt
 *
 *  Compute transitive closure of a digraph and support
 *  reachability queries.
 *
 *  Preprocessing time: O(V(E + V)) time.
 *  Query time: O(1).
 *  Space: O(V^2).
 *
 *  % java TransitiveClosure tinyDG.txt
 *         0  1  2  3  4  5  6  7  8  9 10 11 12
 *  --------------------------------------------
 *    0:   T  T  T  T  T  T
 *    1:      T
 *    2:   T  T  T  T  T  T
 *    3:   T  T  T  T  T  T
 *    4:   T  T  T  T  T  T
 *    5:   T  T  T  T  T  T
 *    6:   T  T  T  T  T  T  T        T  T  T  T
 *    7:   T  T  T  T  T  T  T  T  T  T  T  T  T
 *    8:   T  T  T  T  T  T  T  T  T  T  T  T  T
 *    9:   T  T  T  T  T  T           T  T  T  T
 *   10:   T  T  T  T  T  T           T  T  T  T
 *   11:   T  T  T  T  T  T           T  T  T  T
 *   12:   T  T  T  T  T  T           T  T  T  T
 *
 *************************************************************************/

public class TransitiveClosure {
	private final DirectedDFS[] tc;  // tc[v] = reachable from v

	public TransitiveClosure(Digraph G) {
		tc = new DirectedDFS[G.V()];
		for (int v = 0; v < G.V(); v++)
			tc[v] = new DirectedDFS(G, v);
	}

	public boolean reachable(int v, int w) {
		return tc[v].marked(w);
	}

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

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

		TransitiveClosure tc = new TransitiveClosure(G);

		// print header
		StdOut.print("     ");
		for (int v = 0; v < G.V(); v++)
			StdOut.format("%3d", v);
		StdOut.println();
		StdOut.println("--------------------------------------------");

		// print transitive closure
		for (int v = 0; v < G.V(); v++) {
			StdOut.format("%3d: ", v);
			for (int w = 0; w < G.V(); w++) {
				if (tc.reachable(v, w)) StdOut.format("  T");
				else                    StdOut.format("   ");
			}
			StdOut.println();
		}
	}

}