public static void ShortestPath(SqlInt64 startNode, SqlInt64 endNode, SqlInt32 maxNodesToCheck, out SqlString pathResult, out SqlDouble distResult)
{
Dictionary <long, double> distance = new Dictionary <long, double>(); // curr shortest distance (double) from startNode to (key) node
Dictionary <long, long> previous = new Dictionary <long, long>(); // predecessor values to construct the actual path when done
Dictionary <long, bool> beenAdded = new Dictionary <long, bool>(); // has node been added to the queue yet? Once added, we don't want to add again
long startNodeAsLong = (long)startNode;
long endNodeAsLong = (long)endNode;
int maxNodesToCheckAsInt = (int)maxNodesToCheck;
MyPriorityQueue PQ = new MyPriorityQueue();
//initialize start node
distance[startNodeAsLong] = 0.0; // distance from start node to itself is 0
previous[startNodeAsLong] = -1; // -1 is the code for undefined.
PQ.Enqueue(new NodeDistance(startNodeAsLong, 0.0)); // the queue holds distance information because Enqueue and Dequeue need it to keep queue ordered by priority. alt approach would be to store only node IDs and then do a distance lookup
beenAdded[startNodeAsLong] = true;
double alt = 0.0; //'test distance'
try
{
while (PQ.Count() > 0 && beenAdded.Count < maxNodesToCheckAsInt)
{
NodeDistance u = PQ.Dequeue();// node with shortest distance from start
if (u.nodeID == endNode)
{
break;// found the target end node
}
//fetch all neighbors (v) of u
List <Tuple <long, double> > neighbors = new List <Tuple <long, double> >();
neighbors = FetchNeighbors(u.nodeID);
foreach (var v in neighbors) // if there are no neighbors, this loop will exit immediately
{
if (beenAdded.ContainsKey(v.Item1) == false) //first appearance of node v
{
distance[v.Item1] = double.MaxValue; //stand-in for infinity
previous[v.Item1] = -1; //undefined
PQ.Enqueue(new NodeDistance(v.Item1, double.MaxValue)); //maxValue is a dummy value
beenAdded[v.Item1] = true;
}
//alt = distance[u.nodeID] + 1.0; // if all edge weights are just hops can simplify to this
alt = distance[u.nodeID] + v.Item2; // alt = dist(start-to-u) + dist(u-to-v), so alt is total distance from start to v
if (alt < distance[v.Item1]) // is alt a new, shorter distance from start to v?
{
distance[v.Item1] = alt;
previous[v.Item1] = u.nodeID;
PQ.ChangePriority(v.Item1, alt); // this will change the distance/priority
}
}
}
// extract the shortest path as a string from the previous[] array
pathResult = "NOTREACHABLE"; // default result string
distResult = -1.0; // distance result defaults to -1 == unreachable
if (distance.ContainsKey(endNodeAsLong) == true) // endNode was encountered at some point in the algorithm
{
double sp = distance[endNodeAsLong]; // shortest path distance
if (sp != double.MaxValue) // we have a reachable path
{
pathResult = "";
long currNode = endNodeAsLong;
while (currNode != startNodeAsLong) // construct the path as semicolon delimited string
{
pathResult += currNode.ToString() + ";";
currNode = previous[currNode];
}
pathResult += startNode.ToString(); // tack on the start node
distResult = sp; // the distance result
}
}
}
catch (Exception ex) // typically Out Of Memory or a Command TimeOut
{
pathResult = ex.ToString();
distResult = -1.0;
}
}
