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