package edu.princeton.cs.algs4.ch42;
import edu.princeton.cs.algs4.ch43.EdgeWeightedDigraph;
import edu.princeton.cs.algs4.ch43.EdgeWeightedDirectedCycle;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac Topoological.java
* Dependencies: Digraph.java DepthFirstOrder.java DirectedCycle.java
* EdgeWeightedDigraph.java EdgeWeightedDirectedCycle.java
* SymbolDigraph.java
* Data files: http://algs4.cs.princeton.edu/42directed/jobs.txt
*
* Compute topological ordering of a DAG or edge-weighted DAG.
* Runs in O(E + V) time.
*
* % java Topological jobs.txt "/"
* Calculus
* Linear Algebra
* Introduction to CS
* Programming Systems
* Algorithms
* Theoretical CS
* Artificial Intelligence
* Machine Learning
* Neural Networks
* Robotics
* Scientific Computing
* Computational Biology
* Databases
*
*
*************************************************************************/
/**
* The <tt>Topological</tt> class represents a data type for
* determining a topological order of a directed acyclic graph (DAG).
* Recall, a digraph has a topological order if and only if it is a DAG.
* The <em>hasOrder</em> operation determines whether the digraph has
* a topological order, and if so, the <em>order</em> operation
* returns one.
* <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.
* Afterwards, the <em>hasOrder</em> operation takes constant time;
* the <em>order</em> operation takes time proportional to <em>V</em>.
* <p>
* See {@link DirectedCycle} and {@link edu.princeton.cs.algs4.ch43.EdgeWeightedDirectedCycle} to compute a
* directed cycle if the digraph is not a DAG.
* <p>
* For additional documentation, see <a href="/algs4/42digraph">Section 4.2</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Topological {
private Iterable<Integer> order; // topological order
/**
* Determines whether the digraph <tt>G</tt> has a topological order and, if so,
* finds such a topological order.
* @param G the digraph
*/
public Topological(Digraph G) {
DirectedCycle finder = new DirectedCycle(G);
if (!finder.hasCycle()) {
DepthFirstOrder dfs = new DepthFirstOrder(G);
order = dfs.reversePost();
}
}
/**
* Determines whether the edge-weighted digraph <tt>G</tt> has a topological
* order and, if so, finds such an order.
* @param G the edge-weighted digraph
*/
public Topological(EdgeWeightedDigraph G) {
EdgeWeightedDirectedCycle finder = new EdgeWeightedDirectedCycle(G);
if (!finder.hasCycle()) {
DepthFirstOrder dfs = new DepthFirstOrder(G);
order = dfs.reversePost();
}
}
/**
* Returns a topological order if the digraph has a topologial order,
* and <tt>null</tt> otherwise.
* @return a topological order of the vertices (as an interable) if the
* digraph has a topological order (or equivalently, if the digraph is a DAG),
* and <tt>null</tt> otherwise
*/
public Iterable<Integer> order() {
return order;
}
/**
* Does the digraph have a topological order?
* @return <tt>true</tt> if the digraph has a topological order (or equivalently,
* if the digraph is a DAG), and <tt>false</tt> otherwise
*/
public boolean hasOrder() {
return order != null;
}
/**
* Unit tests the <tt>Topological</tt> data type.
*/
public static void main(String[] args) {
String filename = args[0];
String delimiter = args[1];
SymbolDigraph sg = new SymbolDigraph(filename, delimiter);
Topological topological = new Topological(sg.G());
for (int v : topological.order()) {
StdOut.println(sg.name(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.
*************************************************************************/