80 lines
2.8 KiB
Java
80 lines
2.8 KiB
Java
|
|
||
|
|
|
||
|
|
/*************************************************************************
|
||
|
|
* Compilation: javac DijkstraAllPairsSP.java
|
||
|
|
* 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.
|
||
|
|
*
|
||
|
|
*************************************************************************/
|
||
|
|
|
||
|
|
/**
|
||
|
|
* The DijkstraAllPairsSP class represents a data type for solving the
|
||
|
|
* all-pairs shortest paths problem in edge-weighted digraphs
|
||
|
|
* where the edge weights are nonnegative.
|
||
|
|
*
|
||
|
|
* This implementation runs Dijkstra's algorithm from each vertex.
|
||
|
|
* The constructor takes time proportional to V ( E log V )
|
||
|
|
* and uses space proprtional to V <sup>2</sup>,
|
||
|
|
* where V is the number of vertices and E is the number of edges.
|
||
|
|
* Afterwards, the dist() and hasPath() methods take
|
||
|
|
* constant time and the path() method takes time proportional to the
|
||
|
|
* number of edges in the shortest path returned.
|
||
|
|
*
|
||
|
|
* For additional documentation, see <a href="/algs4/44sp">Section 4.4</a> 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 to every other vertex in
|
||
|
|
* the edge-weighted digraph G .
|
||
|
|
* @param G the edge-weighted digraph
|
||
|
|
* @throws IllegalArgumentException if an edge weight is negative
|
||
|
|
* @throws IllegalArgumentException unless 0 ≤ s ≤ V - 1
|
||
|
|
*/
|
||
|
|
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 s to vertex t .
|
||
|
|
* @param s the source vertex
|
||
|
|
* @param t the destination vertex
|
||
|
|
* @return a shortest path from vertex s to vertex t
|
||
|
|
* as an iterable of edges, and null if no such path
|
||
|
|
*/
|
||
|
|
public Iterable<DirectedEdge> path(int s, int t) {
|
||
|
|
return all[s].pathTo(t);
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Is there a path from the vertex s to vertex t ?
|
||
|
|
* @param s the source vertex
|
||
|
|
* @param t the destination vertex
|
||
|
|
* @return true if there is a path from vertex s
|
||
|
|
* to vertex t , and false otherwise
|
||
|
|
*/
|
||
|
|
public boolean hasPath(int s, int t) {
|
||
|
|
return dist(s, t) < Double.POSITIVE_INFINITY;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Returns the length of a shortest path from vertex s to vertex t .
|
||
|
|
* @param s the source vertex
|
||
|
|
* @param t the destination vertex
|
||
|
|
* @return the length of a shortest path from vertex s to vertex t ;
|
||
|
|
* Double.POSITIVE_INFINITY if no such path
|
||
|
|
*/
|
||
|
|
public double dist(int s, int t) {
|
||
|
|
return all[s].distTo(t);
|
||
|
|
}
|
||
|
|
}
|