//
// This Add method attach an object "data" to a node "n" using
// the BitVector key as path.
//
private void Add(Node n, BitVector key, object data)
{
if (n.Key == null)
{
AddAsChildren(n, key, data);
return;
}
//
// First, calculate the longest common prefix for the key
// and the BitVector stored in this node.
//
int longest = key.LongestCommonPrefix(n.Key);
if (longest == n.Key.Length)
{
//
// If the current node is a perfect prefix of the
// key, then remove the prefix from the key, and
// we continue our walk on the children.
//
key = key.Range(longest, key.Length - longest);
AddAsChildren(n, key, data);
return;
}
else
{
//
// Here, n.Key and key share a common prefix. So we:
//
// - Create a new node with this common prefix
// held there,
//
// - make n.Key and a new node with key as
// children of this new node.
BitVector common = n.Key.Range(0, longest);
Node c1 = new Node();
c1.Key = n.Key.Range(longest, n.Key.Length - longest);
c1.Data = n.Data;
c1.Children = n.Children;
Node c2 = new Node();
c2.Key = key.Range(longest, key.Length - longest);
c2.Data = data;
n.Key = common;
n.Data = null;
n.Children = new ArrayList();
n.Children.Add(c1);
n.Children.Add(c2);
return;
}
}
//
// Returns the object held in the node that best matches our
// key.
//
public object GetBest(BitVector key)
{
Node curnode = Root;
while (curnode != null)
{
if (curnode.Children == null)
return curnode.Data;
// Get the best fitting index
int bestindex = -1;
int bestlength = 0;
for (int i = 0; i < curnode.Children.Count; i++)
{
int b = ((Node) (curnode.Children[i])).Key.LongestCommonPrefix(key);
if (b > bestlength)
{
bestlength = b;
bestindex = i;
}
}
if (bestindex != -1)
{
key = key.Range(bestlength, key.Length - bestlength);
curnode = ((Node) curnode.Children[bestindex]);
if (key.Length == 0)
return curnode.Data;
}
else
{
return curnode.Data;
}
}
return null;
}
