How to bypass Huffman tree and get codes of symbols?

Question

I have a recursive function that bypasses some Huffman tree.

I need to get a string that contains all codes of each symbol.

private void BypassLCR(HuffmanTree node, ref string result)
{
    if (node.Symbol != '\0')
    {
        result += string.Format(" -> {0}| ", node.Symbol);
        return;
    }

    string last = result;
    result += "0";
    BypassLCR(node.Left, ref result);

    last += "1";
    result += last;
    BypassLCR(node.Right, ref result);
}

Property node.Symbol is '\\0' by default when the node is not a leaf.

For example, I have a text containing 'r' , 'o' , 'b' and 'a' symbols. Their codes: 00, 01, 10 and 11 respectively.

Then the output would be:

00 -> r| 01 -> o| 10 -> b| 00 -> r| 01 -> o| 11 -> a|.

I know problem is that last keeps old data about child subtrees. But where in the code to clear it?

Answer 1

Would this work for you?

private string TraverseLCR(HuffmanTree node, string code)
{
    if (IsLeaf(node))
        return $"{code} -> {node.Symbol}| ";

    var leftSubtreeResult = TraverseLCR(node.Left, code + "0");
    var rightSubtreeResult = TraverseLCR(node.Right, code + "1");
    return leftSubtreeResult + rightSubtreeResult;
}

private bool IsLeaf(HuffmanTree node) => node.Symbol != '\0';

Usage:

var allCodes = TraverseLCR(treeRoot, string.Empty);