Sunday, April 17, 2011

A Fractal Tree Implementation

I couldn't resist whipping up a quick implementation of a fractal tree, even though I don't really need it for anything. I'm a sucker for a good algorithm :-)

The code can be amazingly simple. Here's my first cut at insertion:
public void add(T x) {
     Object[] tmp = new Object[] { x };
     int i = 0;
     for (; nodes[i] != null; ++i) {
          tmp = merge(nodes[i], tmp);
          nodes[i] = null;
     nodes[i] = tmp;
merge simply merges two sorted arrays into a new larger array.

This works fine, but it will chew through a lot of memory allocating new arrays. The space will be reclaimed by the garbage collector, but it seems a little wasteful.

So I modified it to pre-allocate the first few levels of small arrays since these are the ones that get the heavy activity. (e.g. the first four levels of size 1, 2, 4, and 8 will handle 15/16 of adds) This complicates the code a bit, but not too badly.

Iteration is quite simple as well - just merging the sorted nodes.

The full code is in SourceForge

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