public static IEnumerable<int?> Find(DirectedWeightedGraph graph, int source)
{
var dist = new int?[graph.NodesCount];
dist[source] = 0;
var closestNodes = new PriorityQueue<int, int>(dist.Select((d, i) => new KeyValuePair<int, int>(i, d.GetValueOrDefault(int.MaxValue))));
var exploredNodes = new HashSet<int>();
while (closestNodes.Count != 0)
{
var node = closestNodes.ExtractHighestPriorityElement();
exploredNodes.Add(node);
foreach (var edge in graph.GetEdges(node).Where(e => !exploredNodes.Contains(e.EndNode)))
{
if (dist[node] != null)
{
var alt = dist[node].Value + edge.Weight;
if (alt < dist[edge.EndNode].GetValueOrDefault(int.MaxValue))
{
dist[edge.EndNode] = alt;
closestNodes.ChangePriority(edge.EndNode, alt);
}
}
}
}
return dist;
}
public void PriorityQueue()
{
PriorityQueue<int> pq = new PriorityQueue<int>(LinqExt.TakeMore);
pq.Enqueue(1, 1);
pq.Enqueue(9, 9);
pq.Enqueue(2, 2);
pq.Enqueue(5, 5);
Assert.IsTrue(pq.First() == 9, "Wrong Priority");
Assert.IsTrue(pq.Dequeue() == 9, "Wrong Priority");
Assert.IsTrue(pq.Dequeue() == 5, "Wrong Priority");
pq.ChangePriority(1, 29);
Assert.IsTrue(pq.First() == 1, "Wrong Priority, 1 should be first priority now with priority 29");
pq.Enqueue(3, 2); //add item with same priority
pq.Enqueue(4, 2); //add item with same priority
Assert.IsTrue(pq.Last() == 4, "Wrong Priority, 4 should be last");
pq.Enqueue(30, 30); // mix case
Assert.IsTrue(pq.First() == 30, "Wrong Priority, 30 should be first priority");
pq.Enqueue(31, 30); // mix case
Assert.IsTrue(pq.First() == 30, "Wrong Priority, 30 should still be first priority");
pq.Enqueue(5, 2); //add item with same priority
pq.Enqueue(6, 2); //add item with same priority
Assert.IsTrue(pq.Last() == 6, "Wrong Priority, 6 should be last");
}
public static int GetMinimumSpanningTreeLength(DirectedWeightedGraph graph)
{
int length = 0;
var dist = new int[graph.NodesCount];
const int StartNode = 0;
dist[StartNode] = 0;
for (int i = 0; i < dist.Length; i++)
{
if (i != StartNode)
{
dist[i] = int.MaxValue;
}
}
var closestNodes = new PriorityQueue<int, int>(dist.Select((d, i) => new KeyValuePair<int, int>(i, d)));
var exploredNodes = new HashSet<int>();
while (exploredNodes.Count != graph.NodesCount)
{
var node = closestNodes.ExtractHighestPriorityElement();
length += dist[node];
exploredNodes.Add(node);
foreach (var edge in graph.GetEdges(node).Where(e => !exploredNodes.Contains(e.EndNode)))
{
var alt = edge.Weight;
if (alt < dist[edge.EndNode])
{
dist[edge.EndNode] = alt;
closestNodes.ChangePriority(edge.EndNode, alt);
}
}
}
return length;
}
