private static int GetTotalBits(Node root)
{
var queue = new Queue<Node>();
queue.Enqueue(root);
var totalBits = 0;
while (queue.Count > 0)
{
var node = queue.Dequeue();
if (node.Left == null && node.Right == null)
{
continue;
}
totalBits += node.Frequency;
if (node.Left != null &&
node.Left.Left != null &&
node.Left.Right != null)
{
queue.Enqueue(node.Left);
}
if (node.Right != null &&
node.Right.Left != null &&
node.Right.Right != null)
{
queue.Enqueue(node.Right);
}
}
return totalBits;
}
public void Build(string text)
{
if (text == null)
{
throw new ArgumentNullException(nameof(text));
}
_root = null;
var frequencies = new Dictionary<char, int>();
_codes.Clear();
foreach (var t in text)
{
int frequency;
if (frequencies.TryGetValue(t, out frequency) == false)
{
frequency = 0;
}
frequencies[t] = frequency + 1;
}
var nodes = frequencies.Select(
symbol => new Node
{
Symbol = symbol.Key,
Frequency = symbol.Value,
}).ToList();
while (nodes.Count > 1)
{
var orderedNodes = nodes
.OrderBy(n => n.Frequency).ToList();
if (orderedNodes.Count >= 2)
{
var taken = orderedNodes.Take(2).ToArray();
var first = taken[0];
var second = taken[1];
var parent = new Node
{
Symbol = '\0',
Frequency = first.Frequency + second.Frequency,
Left = first,
Right = second,
};
nodes.Remove(first);
nodes.Remove(second);
nodes.Add(parent);
}
_root = nodes.FirstOrDefault();
}
foreach (var frequency in frequencies)
{
var bits = Traverse(_root, frequency.Key, new List<bool>());
if (bits == null)
{
throw new InvalidOperationException(string.Format(
"could not traverse '{0}'", frequency.Key));
}
_codes.Add(frequency.Key, new BitArray(bits.ToArray()));
}
TotalBits = GetTotalBits(_root);
}
private static List<bool> Traverse(Node node, char symbol, List<bool> data)
{
if (node.Left == null && node.Right == null)
{
return symbol == node.Symbol ? data : null;
}
if (node.Left != null)
{
var path = new List<bool>();
path.AddRange(data);
path.Add(false);
var left = Traverse(node.Left, symbol, path);
if (left != null)
{
return left;
}
}
if (node.Right != null)
{
var path = new List<bool>();
path.AddRange(data);
path.Add(true);
var right = Traverse(node.Right, symbol, path);
if (right != null)
{
return right;
}
}
return null;
}
