internal void DecreaseKey(int vertex, int updatedDistance)
{
//Find the position where the vertex can be found in HeapNodes[].
// Note this position is not the vertex value;
int vertex_position = VertexPositionInHeap[vertex];
MinHeapNode node = HeapNodes[vertex_position];
HeapNodes[vertex_position].Distance = updatedDistance;
//Fix everything above.
while (vertex_position > 0 && HeapNodes[(vertex_position - 1) / 2].Distance > HeapNodes[vertex_position].Distance)
{
MinHeapNode parentNode = HeapNodes[(vertex_position - 1) / 2];
MinHeapNode node1 = HeapNodes[vertex_position];
//Swap positions of current node and parent node
// int tempPosition = VertexPositionInHeap[node.Vertex];
VertexPositionInHeap[node1.Vertex] = (vertex_position - 1) / 2;
VertexPositionInHeap[parentNode.Vertex] = vertex_position;
//Swap the actual nodes
HeapNodes[(vertex_position - 1) / 2] = node1;
HeapNodes[vertex_position] = parentNode;
vertex_position = (vertex_position - 1) / 2;
}
}
internal void Heapify(int index)
{
int left = 2 * index + 1;
int right = 2 * index + 2;
int min_index = index;
if (left < HeapSize && HeapNodes[left].Distance < HeapNodes[min_index].Distance)
{
min_index = left;
}
if (right < HeapSize && HeapNodes[right].Distance < HeapNodes[min_index].Distance)
{
min_index = right;
}
if (min_index != index)
{
MinHeapNode smallestNode = HeapNodes[min_index];
MinHeapNode currentNode = HeapNodes[index];
//Read this as : Correct position for the node node.Vertex is the r.h.s value.
//Swap positions
VertexPositionInHeap[smallestNode.Vertex] = index;
VertexPositionInHeap[currentNode.Vertex] = min_index;
//Swap nodes
MinHeapNode temp = currentNode;
HeapNodes[index] = HeapNodes[min_index];
HeapNodes[min_index] = temp;
// Fix everything below.
Heapify(min_index);
}
}
public MinHeap(int V)
{
HeapNodes = new MinHeapNode[V];
Capacity = V;
HeapSize = V;
VertexPositionInHeap = new int[V];
for (int i = 0; i < V; i++)
{
HeapNodes[i] = new MinHeapNode(i, Int32.MaxValue);
VertexPositionInHeap[i] = i;
}
//This would be trivial as all the nodes have same distance value
Heapify(0);
}
internal MinHeapNode ExtractMin()
{
if (IsHeapEmpty())
{
return(null);
}
else
{
MinHeapNode first = HeapNodes[0];
MinHeapNode last = HeapNodes[HeapSize - 1];
VertexPositionInHeap[first.Vertex] = HeapSize - 1;
VertexPositionInHeap[last.Vertex] = 0; // Move to top
HeapNodes[0] = last;
HeapNodes[HeapSize - 1] = first;
HeapSize--;
Heapify(0);
return(first);
}
}
