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105 lines
3.5 KiB
Java
105 lines
3.5 KiB
Java
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import edu.princeton.cs.introcs.In;
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import edu.princeton.cs.introcs.StdOut;
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/*************************************************************************
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* Compilation: javac TransitiveClosure.java
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* Execution: java TransitiveClosure filename.txt
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* Dependencies: Digraph.java DepthFirstDirectedPaths.java In.java StdOut.java
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* Data files: http://algs4.cs.princeton.edu/42directed/tinyDG.txt
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*
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* Compute transitive closure of a digraph and support
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* reachability queries.
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*
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* Preprocessing time: O(V(E + V)) time.
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* Query time: O(1).
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* Space: O(V^2).
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*
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* % java TransitiveClosure tinyDG.txt
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* 0 1 2 3 4 5 6 7 8 9 10 11 12
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* --------------------------------------------
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* 0: T T T T T T
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* 1: T
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* 2: T T T T T T
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* 3: T T T T T T
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* 4: T T T T T T
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* 5: T T T T T T
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* 6: T T T T T T T T T T T
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* 7: T T T T T T T T T T T T T
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* 8: T T T T T T T T T T T T T
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* 9: T T T T T T T T T T
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* 10: T T T T T T T T T T
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* 11: T T T T T T T T T T
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* 12: T T T T T T T T T T
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*
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*************************************************************************/
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/**
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* The TransitiveClosure class represents a data type for
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* computing the transitive closure of a digraph.
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*
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* This implementation runs depth-first search from each vertex.
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* The constructor takes time proportional to V ( V + E )
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* (in the worst case) and uses space proportional to V <sup>2</sup>,
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* where V is the number of vertices and E is the number of edges.
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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 TransitiveClosure {
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private DirectedDFS[] tc; // tc[v] = reachable from v
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/**
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* Computes the transitive closure of the digraph G .
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* @param G the digraph
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*/
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public TransitiveClosure(Digraph G) {
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tc = new DirectedDFS[G.V()];
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for (int v = 0; v < G.V(); v++)
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tc[v] = new DirectedDFS(G, v);
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}
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/**
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* Is there a directed path from vertex v to vertex w in the digraph?
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* @param v the source vertex
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* @param w the target vertex
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* @return true if there is a directed path from v to w ,
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* false otherwise
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*/
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public boolean reachable(int v, int w) {
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return tc[v].marked(w);
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}
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/**
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* Unit tests the TransitiveClosure data type.
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*/
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public static void main(String[] args) {
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In in = new In(args[0]);
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Digraph G = new Digraph(in);
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TransitiveClosure tc = new TransitiveClosure(G);
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// print header
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StdOut.print(" ");
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for (int v = 0; v < G.V(); v++)
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StdOut.printf("%3d", v);
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StdOut.println();
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StdOut.println("--------------------------------------------");
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// print transitive closure
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for (int v = 0; v < G.V(); v++) {
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StdOut.printf("%3d: ", v);
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for (int w = 0; w < G.V(); w++) {
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if (tc.reachable(v, w)) StdOut.printf(" T");
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else StdOut.printf(" ");
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}
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StdOut.println();
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}
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}
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}
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