DijkstraAllPairsSP.java
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/******************************************************************************
* 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.
*
******************************************************************************/
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 nonnegative.
* <p>
* This implementation runs Dijkstra's algorithm from each vertex.
* The constructor takes time proportional to <em>V</em> (<em>E</em> log <em>V</em>)
* and uses space proprtional to <em>V</em><sup>2</sup>,
* where <em>V</em> is the number of vertices and <em>E</em> is the number of edges.
* Afterwards, the {@code dist()} and {@code hasPath()} methods take
* constant time and the {@code path()} method takes time proportional to the
* number of edges in the shortest path returned.
* <p>
* For additional documentation,
* see <a href="http://algs4.cs.princeton.edu/44sp">Section 4.4</a> of
* <i>Algorithms, 4th Edition</i> 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 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<DirectedEdge> 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));
}
}
/******************************************************************************
* Copyright 2002-2016, 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.
******************************************************************************/