/// <summary>
/// Single-source weighted shortest-path algorithm.
/// The Dijkstra algorithm is not used by Labyrinth but was included in the
/// previous code and has been updated to use a custom priority queue.
///
/// This code conversion is untested.
/// </summary>
/// <param name="startName">the integer name of the starting Vertex</param>
public void Dijkstra(T startName)
{
PriorityQueue <SearchPath <T> > pq = new PriorityQueue <SearchPath <T> >( );
if (!vertexMap.ContainsKey(startName))
{
throw new Exception("Start not found!");
}
Vertex <T> start = vertexMap[startName];
if (start == null)
{
throw new Exception("Start vertex not found");
}
ClearAll( );
pq.Enqueue(new SearchPath <T>(start, 0));
start.dist = 0;
int nodesSeen = 0;
while (!pq.IsEmpty && nodesSeen < vertexMap.Count)
{
SearchPath <T> vrec = pq.Dequeue();
Vertex <T> v = vrec.dest;
if (v.scratch != 0) // already processed v
{
continue;
}
v.scratch = 1;
nodesSeen++;
foreach (Edge <T> e in v.adj)
{
Vertex <T> w = e.dest;
double cvw = e.cost;
if (cvw < 0)
{
throw new Exception("Graph has negative edges");
}
if (w.dist > v.dist + cvw)
{
w.dist = v.dist + cvw;
w.prev = v;
pq.Enqueue(new SearchPath <T>(w, w.dist));
}
}
}
}
/// <summary>
/// CompareTo is required for the implementation of IComparable.
/// It allows comparing one SearchPath with another based on cost.
/// </summary>
/// <param name="rhs">the right hand side SearchPath</param>
/// <returns>-1 for lesser cost, 0 for same, or 1 for greater cost</returns>
public int CompareTo(SearchPath <T> rhs)
{
double otherCost = rhs.cost;
return(cost <otherCost ? -1 : cost> otherCost ? 1 : 0);
}
