/******************************************************************************
* Compilation: javac DijkstraAllPairsSP.java
* Execution: none
* Dependencies: EdgeWeightedDigraph.java Dijkstra.java
*
* Dijkstra's algorithm run from each vertex.
* Takes time proportional to E V log V and space proportional to EV.
*
* % java DijkstraAllPairsSP tinyEWD.txt
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code DijkstraAllPairsSP} class represents a data type for solving the
* all-pairs shortest paths problem in edge-weighted digraphs
* where the edge weights are non-negative.
*
* This implementation runs Dijkstra's algorithm from each vertex.
* The constructor takes Θ(V (E log V)) time
* in the worst case, where V is the number of vertices and
* E is the number of edges.
* Each instance method takes Θ(1) time.
* It uses Θ(V2) extra space (not including the
* edge-weighted digraph).
*
* For additional documentation,
* see Section 4.4 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class DijkstraAllPairsSP {
private DijkstraSP[] all;
/**
* Computes a shortest paths tree from each vertex to every other vertex in
* the edge-weighted digraph {@code G}.
* @param G the edge-weighted digraph
* @throws IllegalArgumentException if an edge weight is negative
* @throws IllegalArgumentException unless {@code 0 <= s < V}
*/
public DijkstraAllPairsSP(EdgeWeightedDigraph G) {
all = new DijkstraSP[G.V()];
for (int v = 0; v < G.V(); v++)
all[v] = new DijkstraSP(G, v);
}
/**
* Returns a shortest path from vertex {@code s} to vertex {@code t}.
* @param s the source vertex
* @param t the destination vertex
* @return a shortest path from vertex {@code s} to vertex {@code t}
* as an iterable of edges, and {@code null} if no such path
* @throws IllegalArgumentException unless {@code 0 <= s < V}
* @throws IllegalArgumentException unless {@code 0 <= t < V}
*/
public Iterable path(int s, int t) {
validateVertex(s);
validateVertex(t);
return all[s].pathTo(t);
}
/**
* Is there a path from the vertex {@code s} to vertex {@code t}?
* @param s the source vertex
* @param t the destination vertex
* @return {@code true} if there is a path from vertex {@code s}
* to vertex {@code t}, and {@code false} otherwise
* @throws IllegalArgumentException unless {@code 0 <= s < V}
* @throws IllegalArgumentException unless {@code 0 <= t < V}
*/
public boolean hasPath(int s, int t) {
validateVertex(s);
validateVertex(t);
return dist(s, t) < Double.POSITIVE_INFINITY;
}
/**
* Returns the length of a shortest path from vertex {@code s} to vertex {@code t}.
* @param s the source vertex
* @param t the destination vertex
* @return the length of a shortest path from vertex {@code s} to vertex {@code t};
* {@code Double.POSITIVE_INFINITY} if no such path
* @throws IllegalArgumentException unless {@code 0 <= s < V}
* @throws IllegalArgumentException unless {@code 0 <= t < V}
*/
public double dist(int s, int t) {
validateVertex(s);
validateVertex(t);
return all[s].distTo(t);
}
// throw an IllegalArgumentException unless {@code 0 <= v < V}
private void validateVertex(int v) {
int V = all.length;
if (v < 0 || v >= V)
throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
}
/**
* Unit tests the {@code DijkstraAllPairsSP} data type.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
// read edge-weighted digraph
In in = new In(args[0]);
EdgeWeightedDigraph G = new EdgeWeightedDigraph(in);
// compute shortest paths between all pairs of vertices
DijkstraAllPairsSP spt = new DijkstraAllPairsSP(G);
// print all-pairs shortest path distances
StdOut.printf(" ");
for (int v = 0; v < G.V(); v++) {
StdOut.printf("%6d ", v);
}
StdOut.println();
for (int v = 0; v < G.V(); v++) {
StdOut.printf("%3d: ", v);
for (int w = 0; w < G.V(); w++) {
if (spt.hasPath(v, w)) StdOut.printf("%6.2f ", spt.dist(v, w));
else StdOut.printf(" Inf ");
}
StdOut.println();
}
StdOut.println();
// print all-pairs shortest paths
for (int v = 0; v < G.V(); v++) {
for (int w = 0; w < G.V(); w++) {
if (spt.hasPath(v, w)) {
StdOut.printf("%d to %d (%5.2f) ", v, w, spt.dist(v, w));
for (DirectedEdge e : spt.path(v, w))
StdOut.print(e + " ");
StdOut.println();
}
else {
StdOut.printf("%d to %d no path\n", v, w);
}
}
}
}
}
/******************************************************************************
* Copyright 2002-2022, 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.
******************************************************************************/