/// <summary>
/// Decodes a given binary path to represent it's string value
/// </summary>
/// <param name="bits">BitArray for traversing the tree</param>
/// <returns></returns>
public string Decode(BitArray bits)
{
HuffmanNode current = Root;
string decodedString = string.Empty;
foreach (bool bit in bits)
{
//Find the correct current node depending on the bit set or not set.
current = (bit ? current.Right ?? current : current.Left ?? current);
if (current.IsLeaf())
{
decodedString += current.Character;
current = Root;
}
}
return(decodedString);
}
/// <summary>
/// Builds the Huffman tree
/// </summary>
public void BuildTree()
{
if (!Frequencies.FrequencyTable.Any())
{
throw new ArgumentNullException("Frequency table is empty");
}
_nodes.Clear(); //As we build a new tree, first make sure it's clean :)
foreach (KeyValuePair <char, int> symbol in Frequencies.FrequencyTable)
{
_nodes.Add(new HuffmanNode()
{
Character = symbol.Key, Frequency = symbol.Value
});
}
while (_nodes.Count > 1)
{
List <HuffmanNode> orderedNodes = _nodes.OrderBy(node => node.Frequency).ToList();
if (orderedNodes.Count >= 2)
{
List <HuffmanNode> takenNodes = orderedNodes.Take(2).ToList();
HuffmanNode parent = new HuffmanNode()
{
Character = null,
Frequency = takenNodes[0].Frequency + takenNodes[1].Frequency,
Left = takenNodes[0],
Right = takenNodes[1]
};
//Remove the childnodes from the original node list and add the new parent node
_nodes.Remove(takenNodes[0]);
_nodes.Remove(takenNodes[1]);
_nodes.Add(parent);
}
}
Root = _nodes.FirstOrDefault();
}
/// <summary>
/// Determines whether a given Huffman node is a leaf or not.
/// A node is considered to be a leaf when it has no childnodes
/// </summary>
/// <param name="node">A huffman node</param>
/// <returns>True if no children are left, false otherwise</returns>
public static bool IsLeaf(this HuffmanNode node)
{
return (null == node.Left && null == node.Right);
}
