You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
120 lines
3.8 KiB
Java
120 lines
3.8 KiB
Java
|
|
|
|
import edu.princeton.cs.introcs.StdOut;
|
|
|
|
/*************************************************************************
|
|
* 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 Topological 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 hasOrder operation determines whether the digraph has
|
|
* a topological order, and if so, the order operation
|
|
* returns one.
|
|
*
|
|
* 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.
|
|
* Afterwards, the hasOrder operation takes constant time;
|
|
* the order operation takes time proportional to V .
|
|
*
|
|
* See {@link DirectedCycle} and {@link EdgeWeightedDirectedCycle} to compute a
|
|
* directed cycle if the digraph is not a DAG.
|
|
*
|
|
* For additional documentation, see <a href="/algs4/42digraph">Section 4.2</a> of
|
|
* Algorithms, 4th Edition 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 G 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 G 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 null 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 null otherwise
|
|
*/
|
|
public Iterable<Integer> order() {
|
|
return order;
|
|
}
|
|
|
|
/**
|
|
* Does the digraph have a topological order?
|
|
* @return true if the digraph has a topological order (or equivalently,
|
|
* if the digraph is a DAG), and false otherwise
|
|
*/
|
|
public boolean hasOrder() {
|
|
return order != null;
|
|
}
|
|
|
|
/**
|
|
* Unit tests the Topological 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));
|
|
}
|
|
}
|
|
|
|
}
|