package edu.princeton.cs.algs4.ch42;
import edu.princeton.cs.algs4.ch13.Bag;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac DirectedDFS.java
* Execution: java DirectedDFS V E
* Dependencies: Digraph.java Bag.java In.java StdOut.java
* Data files: http://www.cs.princeton.edu/algs4/42directed/tinyDG.txt
*
* Determine single-source or multiple-source reachability in a digraph
* using depth first search.
* Runs in O(E + V) time.
*
* % java DirectedDFS tinyDG.txt 1
* 1
*
* % java DirectedDFS tinyDG.txt 2
* 0 1 2 3 4 5
*
* % java DirectedDFS tinyDG.txt 1 2 6
* 0 1 2 3 4 5 6 8 9 10 11 12
*
*************************************************************************/
/**
* The <tt>DirectedDFS</tt> class represents a data type for
* determining the vertices reachable from a given source vertex <em>s</em>
* (or set of source vertices) in a digraph. For versions that find the paths,
* see {@link edu.princeton.cs.algs4.DepthFirstDirectedPaths} and {@link edu.princeton.cs.algs4.BreadthFirstDirectedPaths}.
* <p>
* This implementation uses depth-first search.
* The constructor takes time proportional to <em>V</em> + <em>E</em>
* (in the worst case),
* where <em>V</em> is the number of vertices and <em>E</em> is the number of edges.
* <p>
* For additional documentation, see <a href="/algs4/41graph">Section 4.1</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class DirectedDFS {
private boolean[] marked; // marked[v] = true if v is reachable
// from source (or sources)
private int count; // number of vertices reachable from s
/**
* Computes the vertices in digraph <tt>G</tt> that are
* reachable from the source vertex <tt>s</tt>.
* @param G the digraph
* @param s the source vertex
*/
public DirectedDFS(Digraph G, int s) {
marked = new boolean[G.V()];
dfs(G, s);
}
/**
* Computes the vertices in digraph <tt>G</tt> that are
* connected to any of the source vertices <tt>sources</tt>.
* @param G the graph
* @param sources the source vertices
*/
public DirectedDFS(Digraph G, Iterable<Integer> sources) {
marked = new boolean[G.V()];
for (int v : sources) {
if (!marked[v]) dfs(G, v);
}
}
private void dfs(Digraph G, int v) {
count++;
marked[v] = true;
for (int w : G.adj(v)) {
if (!marked[w]) dfs(G, w);
}
}
/**
* Is there a directed path from the source vertex (or any
* of the source vertices) and vertex <tt>v</tt>?
* @param v the vertex
* @return <tt>true</tt> if there is a directed path, <tt>false</tt> otherwise
*/
public boolean marked(int v) {
return marked[v];
}
/**
* Returns the number of vertices reachable from the source vertex
* (or source vertices).
* @return the number of vertices reachable from the source vertex
* (or source vertices)
*/
public int count() {
return count;
}
/**
* Unit tests the <tt>DirectedDFS</tt> data type.
*/
public static void main(String[] args) {
// read in digraph from command-line argument
In in = new In(args[0]);
Digraph G = new Digraph(in);
// read in sources from command-line arguments
Bag<Integer> sources = new Bag<Integer>();
for (int i = 1; i < args.length; i++) {
int s = Integer.parseInt(args[i]);
sources.add(s);
}
// multiple-source reachability
DirectedDFS dfs = new DirectedDFS(G, sources);
// print out vertices reachable from sources
for (int v = 0; v < G.V(); v++) {
if (dfs.marked(v)) StdOut.print(v + " ");
}
StdOut.println();
}
}
/*************************************************************************
* Copyright 2002-2012, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4-package.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4-package.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4-package.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with algs4-package.jar. If not, see http://www.gnu.org/licenses.
*************************************************************************/