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/******************************************************************************
* Compilation: javac DepthFirstDirectedPaths.java
* Execution: java DepthFirstDirectedPaths digraph.txt s
* Dependencies: Digraph.java Stack.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 reachability in a digraph from a given vertex using
* depth-first search.
* Runs in O(E + V) time.
*
* % java DepthFirstDirectedPaths 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
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code DepthFirstDirectedPaths} class represents a data type for finding
* directed paths from a source vertex s to every
* other vertex in the digraph.
*
* This implementation uses depth-first search.
* The constructor takes time proportional to V + E,
* where V is the number of vertices and E is the number of edges.
* Each call to {@link #hasPathTo(int)} takes constant time;
* each call to {@link #pathTo(int)} takes time proportional to the length
* of the path returned.
* It uses extra space (not including the graph) proportional to V.
*
* See {@link DepthFirstDirectedPaths} for a nonrecursive implementation.
* 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 DepthFirstDirectedPaths {
private boolean[] marked; // marked[v] = true iff 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 {@code s} to every other vertex in digraph {@code G}.
* @param G the digraph
* @param s the source vertex
* @throws IllegalArgumentException unless {@code 0 <= s < V}
*/
public DepthFirstDirectedPaths(Digraph G, int s) {
marked = new boolean[G.V()];
edgeTo = new int[G.V()];
this.s = s;
validateVertex(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 {@code s} to vertex {@code v}?
* @param v the vertex
* @return {@code true} if there is a directed path from the source
* vertex {@code s} to vertex {@code v}, {@code false} otherwise
* @throws IllegalArgumentException unless {@code 0 <= v < V}
*/
public boolean hasPathTo(int v) {
validateVertex(v);
return marked[v];
}
/**
* Returns a directed path from the source vertex {@code s} to vertex {@code v}, or
* {@code null} if no such path.
* @param v the vertex
* @return the sequence of vertices on a directed path from the source vertex
* {@code s} to vertex {@code v}, as an Iterable
* @throws IllegalArgumentException unless {@code 0 <= v < V}
*/
public Iterable pathTo(int v) {
validateVertex(v);
if (!hasPathTo(v)) return null;
Stack path = new Stack();
for (int x = v; x != s; x = edgeTo[x])
path.push(x);
path.push(s);
return path;
}
// 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));
}
/**
* Unit tests the {@code DepthFirstDirectedPaths} data type.
*
* @param args the command-line arguments
*/
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 2002-2018, 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.
******************************************************************************/