public void query_vp(VPNode <T> root, T who, int maxd, List <T> ret)
{
if (root.linear)
{
for (int i = 0; i < root.count; i++)
{
if (_distFunc(who, root.keys[i]) <= maxd)
{
ret.Add(root.keys[i]);
}
}
return;
}
int d = _distFunc(root.vantage, who);
int thr = root.threshold;
if (d <= (maxd + thr))
{
if (root.near != null)
{
query_vp(root.near, who, maxd, ret);
}
if (d < maxd)
{
ret.Add(root.vantage);
}
}
if ((d + maxd) > thr && root.far != null)
{
query_vp(root.far, who, maxd, ret);
}
}
public VPNode <T> make_vp(List <T> keys)
{
int n = keys.Count;
VPNode <T> root = new VPNode <T>();
if (n <= max_linear || n <= 1)
{
root.linear = true;
root.count = (uint)n;
root.keys = new List <T>();
root.keys.AddRange(keys);
return(root);
}
T rootkey = keys[0];
root.linear = false;
root.threshold = 0;
root.vantage = rootkey;
// count keys inside the given ball
int [] dcnt = new int[MAX_DISTANCE + 1];
for (int i = 0; i <= MAX_DISTANCE; i++)
{
dcnt[i] = 0;
}
for (int i = 0; i < n; i++)
{
int dist = _distFunc(rootkey, keys[i]);
dcnt[dist]++;
}
int a = 0;
for (int i = 0; i <= MAX_DISTANCE; i++)
{
a += dcnt[i];
dcnt[i] = a;
}
Debug.Assert(a == n);
int median = dcnt[0] + (n - dcnt[0]) / 2;
int k = 1;
for (; k <= MAX_DISTANCE; k++)
{
if (dcnt[k] > median)
{
break;
}
}
if (k != 1 && ((median - dcnt[k - 1]) <= (dcnt[k] - median)))
{
k--;
}
int nnear = dcnt[k] - dcnt[0];
int nfar = n - dcnt[k];
// Sort keys into near and far sets
List <T> nearKeys = new List <T>();
List <T> farKeys = new List <T>();
for (int i = 0; i < n; i++)
{
if (keys[i].Equals(rootkey))
{
continue;
}
if (_distFunc(rootkey, keys[i]) <= k)
{
nearKeys.Add(keys[i]);
}
else
{
farKeys.Add(keys[i]);
}
}
//Debug.Assert(nearKeys.Count == nnear);
Debug.Assert(farKeys.Count == nfar);
root.threshold = k;
if (nnear > 0)
{
root.near = make_vp(nearKeys);
}
if (nfar > 0)
{
root.far = make_vp(farKeys);
}
return(root);
}
