Huffman Trees - finding the prefix codes

Hi all,

I understand the underlying concepts behind the generation of a Huffman Tree and can do it on paper; the problem is converting the concept into a routine/program.

This is what I'm hoping to accomplish: http://huffman.ooz.ie/?text=This%20is%20a%20test%20string

So far I've been able to create and organise the frequency table. I don't know what the next step is. I know, however, that I need to begin with the two lowest frequencies and sum them up then repeat. I'm uncertain as to how I can accomplish this and generate a tree. A 2D, 3D array? Some queer data type?

Any help would be highly appreciated, thanks!

#include <Array.au3>

$time = TimerInit()
$str = "This is a test string"
$var = StringSplit($str, "")

Dim $trie[1][2]
$trie[0][0] = $str
$trie[0][1] = $var[0]

For $i = 1 To $var[0]
    For $j = 1 To UBound($trie)-1
        If $trie[$j][0] == $var[$i] Then
            $trie[$j][1] += 1
            ContinueLoop 2
        EndIf
    Next

    ReDim $trie[$j + 1][2]
    $trie[$j][0] = $var[$i]
    $trie[$j][1] = 1
Next

ConsoleWrite("Execution time: " & TimerDiff($time) & "ms" & @LF)

_ArraySort($trie, 1, 0, 0, 1)
_ArrayDisplay($trie)

$trie[UBound($trie)-2][0] = $trie[UBound