DijkstraAllPairsSP.h

#ifndef CH4_DIJKSTRAALLPAIRSSP_H
#define CH4_DIJKSTRAALLPAIRSSP_H

#include "../head/DijkstraSP.h"

/**
 *  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="https://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
 */
class DijkstraAllPairsSP {
public:
    /**
     * 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}
     */
    DijkstraAllPairsSP(EdgeWeightedDigraph &G) : all(G.V_()) {
        for (int v = 0; v < G.V_(); v++)
            all[v] = 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}
     */
    forward_list<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}
     */
    bool hasPath(int s, int t) {
        validateVertex(s);
        validateVertex(t);
        return dist(s, t) < numeric_limits<double>::max();
    }

    /**
     * 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}
     */
    double dist(int s, int t) {
        validateVertex(s);
        validateVertex(t);
        return all[s].distTo_(t);
    }

private:
    // throw an IllegalArgumentException unless {@code 0 <= v < V}
    void validateVertex(int v) {
        int V = all.size();
        if (v < 0 || v >= V)
            throw runtime_error("vertex " + to_string(v) + " is not between 0 and " + to_string(V - 1));
    }

private:
    vector<DijkstraSP> all;
};

#endif //CH4_DIJKSTRAALLPAIRSSP_H