private VPTreeNode CreateNode(int lowerIndex, int upperIndex)
{
if (upperIndex == lowerIndex)
{
return(null);
}
VPTreeNode node = new VPTreeNode(lowerIndex);
if (upperIndex - lowerIndex > 1)
{
Swap(data, lowerIndex, this.randomizer.Next(lowerIndex + 1, upperIndex));
int medianIndex = (upperIndex + lowerIndex) / 2;
int comparsion(T i1, T i2) => Comparer <int> .Default.Compare(this.analyzer.CalculateDistance(data[lowerIndex], i1),
this.analyzer.CalculateDistance(data[lowerIndex], i2));
NthElement(data, lowerIndex + 1, medianIndex, upperIndex - 1, comparsion);
node.radius = this.analyzer.CalculateDistance(this.data[lowerIndex], this.data[medianIndex]);
node.left = CreateNode(lowerIndex + 1, medianIndex);
node.right = CreateNode(medianIndex, upperIndex);
}
return(node);
}
private void Search(VPTreeNode node, T target, List <HeapItem> closestHits)
{
if (node == null)
{
return;
}
int dist = this.analyzer.SearchComparator(this.data[node.dataIndex], target);
if (dist <= this.tau)
{
closestHits.Add(new HeapItem(node.dataIndex, dist));
}
if (node.left == null && node.right == null)
{
return;
}
if (dist < node.radius)
{
if (dist - this.tau <= node.radius)
{
this.Search(node.left, target, closestHits);
}
if (dist + this.tau >= node.radius)
{
this.Search(node.right, target, closestHits);
}
}
else
{
if (dist + this.tau >= node.radius)
{
this.Search(node.right, target, closestHits);
}
if (dist - this.tau <= node.radius)
{
this.Search(node.left, target, closestHits);
}
}
}
/// <summary>
/// Create VP-tree using INodeAnalyzer.CalculateDistance for node distance calculating
/// </summary>
public void Create(T[] data, INodeAnalyzer <T> analyzer)
{
this.data = data;
this.analyzer = analyzer;
this.root = this.CreateNode(0, data.Length);
}
