public int GetMinAllPairsShortestPaths(Dictionary <int, NodeWeighted> graph)
{
var vertCount = graph.Count;
var min = int.MaxValue;
foreach (var startingNode in graph)
{
var sourceId = startingNode.Key;
var sourceJohnsonVal = graph[sourceId].JohnsonsValue;
var visitedNodesCount = 0;
var closestUnvisitedNodes = new MinHeapUniversal <NodeWeighted>();
var sourceNode = graph[sourceId];
sourceNode.Value = 0;
foreach (var node in graph)
{
closestUnvisitedNodes.InsertElement(node.Value);
}
while (visitedNodesCount++ != vertCount)
{
var lastAddedNode = closestUnvisitedNodes.ExtractMinElement();
lastAddedNode.HeapIndex = 0;
if (lastAddedNode.Id != sourceId)
{
var adjustedPathValue = lastAddedNode.Value + lastAddedNode.JohnsonsValue - sourceJohnsonVal;
min = Math.Min(min, adjustedPathValue);
}
foreach (var nodeWeightTuple in lastAddedNode.Neighbours)
{
var(neighbour, edgeLength) = nodeWeightTuple;
if (neighbour.HeapIndex == 0)
{
continue;
}
var pathLength = edgeLength + lastAddedNode.Value;
closestUnvisitedNodes.TryDecreaseKey(neighbour.HeapIndex, pathLength);
}
lastAddedNode.Value = Globals.DefaultDijkstraValue;
}
}
return(min);
}
public int[] GetShortestPaths(Dictionary <int, NodeWeighted> graph, int startingVertex)
{
var visitedNodesCount = 1;
var closestUnvisitedNodes = new MinHeapUniversal <NodeWeighted>();
var pathLengths = new int[graph.Count + 1];
var firstNode = graph[startingVertex];
firstNode.Value = 0;
pathLengths[startingVertex] = 0;
var lastAddedNode = firstNode;
lastAddedNode.Visit();
while (visitedNodesCount++ != graph.Count - 1)
{
var unvisitedHeadNodes = lastAddedNode.Neighbours.FindAll(x => !x.Item1.IsVisited);
foreach (var nodeWeightTuple in unvisitedHeadNodes)
{
var(neighbour, edgeLength) = nodeWeightTuple;
var pathLength = edgeLength + lastAddedNode.Value;
var isNodeInHeap = neighbour.HeapIndex != 0;
if (isNodeInHeap)
{
closestUnvisitedNodes.TryDecreaseKey(neighbour.HeapIndex, pathLength);
}
else
{
neighbour.Value = pathLength;
closestUnvisitedNodes.InsertElement(neighbour);
}
}
if (closestUnvisitedNodes.GetHeapSize() != 0)
{
lastAddedNode = closestUnvisitedNodes.ExtractMinElement();
lastAddedNode.Visit();
lastAddedNode.HeapIndex = 0;
pathLengths[lastAddedNode.Id] = lastAddedNode.Value;
}
}
return(pathLengths);
}
// input - connected graph. Task - find collection of cheapest edges to connect all nodes
public List <Tuple <int, int, int> > GetMinimumSpanningTree(Dictionary <int, NodeWeighted> graph)
{
var nodesCount = graph.Count;
var cheapestEdgesHeap = new MinHeapUniversal <NodeWeighted>();
var msTree = new List <Tuple <int, int, int> >();
var cheapestNode = graph.Values.First();
cheapestNode.Visit();
nodesCount--;
while (nodesCount != 0)
{
var unvisitedNeighbours = cheapestNode.Neighbours.Where(x => !x.Item1.IsVisited);
foreach (var nodeTuple in unvisitedNeighbours)
{
var currentNode = nodeTuple.Item1;
var edgeWeight = nodeTuple.Item2;
if (currentNode.HeapIndex == 0)
{
currentNode.Parent = cheapestNode;
currentNode.Value = edgeWeight;
cheapestEdgesHeap.InsertElement(currentNode);
continue;
}
if (cheapestEdgesHeap.TryDecreaseKey(currentNode.HeapIndex, edgeWeight))
{
currentNode.Parent = cheapestNode;
}
}
cheapestNode = cheapestEdgesHeap.ExtractMinElement();
cheapestNode.Visit();
var edge = new Tuple <int, int, int>(cheapestNode.Parent.Id, cheapestNode.Id, cheapestNode.Value);
msTree.Add(edge);
nodesCount--;
}
return(msTree);
}