/******************************************************************************
* Compilation: javac DirectedDFS.java
* Execution: java DirectedDFS digraph.txt s
* Dependencies: Digraph.java Bag.java In.java StdOut.java
* Data files: https://algs4.cs.princeton.edu/42digraph/tinyDG.txt
* https://algs4.cs.princeton.edu/42digraph/mediumDG.txt
* https://algs4.cs.princeton.edu/42digraph/largeDG.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
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code DirectedDFS} class represents a data type for
* determining the vertices reachable from a given source vertex s
* (or set of source vertices) in a digraph. For versions that find the paths,
* see {@link DepthFirstDirectedPaths} and {@link BreadthFirstDirectedPaths}.
*
* This implementation uses depth-first search.
* The constructor takes time proportional to V + E
* (in the worst case),
* where V is the number of vertices and E is the number of edges.
* Each instance method takes Θ(1) time.
* It uses Θ(V) extra space (not including the digraph).
*
* For additional documentation,
* see Section 4.2 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class DirectedDFS {
private boolean[] marked; // marked[v] = true iff v is reachable from source(s)
private int count; // number of vertices reachable from source(s)
/**
* Computes the vertices in digraph {@code G} that are
* reachable from the source vertex {@code s}.
* @param G the digraph
* @param s the source vertex
* @throws IllegalArgumentException unless {@code 0 <= s < V}
*/
public DirectedDFS(Digraph G, int s) {
marked = new boolean[G.V()];
validateVertex(s);
dfs(G, s);
}
/**
* Computes the vertices in digraph {@code G} that are
* connected to any of the source vertices {@code sources}.
* @param G the graph
* @param sources the source vertices
* @throws IllegalArgumentException if {@code sources} is {@code null}
* @throws IllegalArgumentException if {@code sources} contains no vertices
* @throws IllegalArgumentException unless {@code 0 <= s < V}
* for each vertex {@code s} in {@code sources}
*/
public DirectedDFS(Digraph G, Iterable sources) {
marked = new boolean[G.V()];
validateVertices(sources);
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 {@code v}?
* @param v the vertex
* @return {@code true} if there is a directed path, {@code false} otherwise
* @throws IllegalArgumentException unless {@code 0 <= v < V}
*/
public boolean marked(int v) {
validateVertex(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;
}
// throw an IllegalArgumentException unless {@code 0 <= v < V}
private void validateVertex(int v) {
int V = marked.length;
if (v < 0 || v >= V)
throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
}
// throw an IllegalArgumentException if vertices is null, has zero vertices,
// or has a vertex not between 0 and V-1
private void validateVertices(Iterable vertices) {
if (vertices == null) {
throw new IllegalArgumentException("argument is null");
}
int vertexCount = 0;
for (Integer v : vertices) {
vertexCount++;
if (v == null) {
throw new IllegalArgumentException("vertex is null");
}
validateVertex(v);
}
if (vertexCount == 0) {
throw new IllegalArgumentException("zero vertices");
}
}
/**
* Unit tests the {@code DirectedDFS} data type.
*
* @param args the command-line arguments
*/
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 sources = new Bag();
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 2002-2022, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4.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.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.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.jar. If not, see http://www.gnu.org/licenses.
******************************************************************************/