package edu.princeton.cs.algs4;
import edu.princeton.cs.algs4.ch13.Stack;
import edu.princeton.cs.algs4.ch42.Digraph;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac DepthFirstDirectedPaths.java
* Execution: java DepthFirstDirectedPaths G s
* Dependencies: Digraph.java Stack.java
*
* Determine reachability in a digraph from a given vertex using
* depth first search.
* Runs in O(E + V) time.
*
* % tinyDG.txt 3
* 3 to 0: 3-5-4-2-0
* 3 to 1: 3-5-4-2-0-1
* 3 to 2: 3-5-4-2
* 3 to 3: 3
* 3 to 4: 3-5-4
* 3 to 5: 3-5
* 3 to 6: not connected
* 3 to 7: not connected
* 3 to 8: not connected
* 3 to 9: not connected
* 3 to 10: not connected
* 3 to 11: not connected
* 3 to 12: not connected
*
*************************************************************************/
/**
* The <tt>DepthFirstDirectedPaths</tt> class represents a data type for finding
* directed paths from a source vertex <em>s</em> to every
* other vertex in the digraph.
* <p>
* This implementation uses depth-first search.
* The constructor takes time proportional to <em>V</em> + <em>E</em>,
* where <em>V</em> is the number of vertices and <em>E</em> is the number of edges.
* It uses extra space (not including the graph) proportional to <em>V</em>.
* <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 DepthFirstDirectedPaths {
private boolean[] marked; // marked[v] = true if v is reachable from s
private int[] edgeTo; // edgeTo[v] = last edge on path from s to v
private final int s; // source vertex
/**
* Computes a directed path from <tt>s</tt> to every other vertex in digraph <tt>G</tt>.
* @param G the digraph
* @param s the source vertex
*/
public DepthFirstDirectedPaths(Digraph G, int s) {
marked = new boolean[G.V()];
edgeTo = new int[G.V()];
this.s = s;
dfs(G, s);
}
private void dfs(Digraph G, int v) {
marked[v] = true;
for (int w : G.adj(v)) {
if (!marked[w]) {
edgeTo[w] = v;
dfs(G, w);
}
}
}
/**
* Is there a directed path from the source vertex <tt>s</tt> to vertex <tt>v</tt>?
* @param v the vertex
* @return <tt>true</tt> if there is a directed path from the source
* vertex <tt>s</tt> to vertex <tt>v</tt>, <tt>false</tt> otherwise
*/
public boolean hasPathTo(int v) {
return marked[v];
}
/**
* Returns a directed path from the source vertex <tt>s</tt> to vertex <tt>v</tt>, or
* <tt>null</tt> if no such path.
* @param v the vertex
* @return the sequence of vertices on a directed path from the source vertex
* <tt>s</tt> to vertex <tt>v</tt>, as an Iterable
*/
public Iterable<Integer> pathTo(int v) {
if (!hasPathTo(v)) return null;
Stack<Integer> path = new Stack<Integer>();
for (int x = v; x != s; x = edgeTo[x])
path.push(x);
path.push(s);
return path;
}
/**
* Unit tests the <tt>DepthFirstDirectedPaths</tt> data type.
*/
public static void main(String[] args) {
In in = new In(args[0]);
Digraph G = new Digraph(in);
// StdOut.println(G);
int s = Integer.parseInt(args[1]);
DepthFirstDirectedPaths dfs = new DepthFirstDirectedPaths(G, s);
for (int v = 0; v < G.V(); v++) {
if (dfs.hasPathTo(v)) {
StdOut.printf("%d to %d: ", s, v);
for (int x : dfs.pathTo(v)) {
if (x == s) StdOut.print(x);
else StdOut.print("-" + x);
}
StdOut.println();
}
else {
StdOut.printf("%d to %d: not connected\n", s, v);
}
}
}
}
/*************************************************************************
* 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.
*************************************************************************/