static string decode(bool[] encoded_text, Node node)
{
Node node_a = node;
StringBuilder builder = new StringBuilder();
for (int i = 0; i < encoded_text.Length;)
{
while (!node.IsEnd)
{
if (encoded_text[i++])
node = node.B;
else
node = node.A;
}
builder.Append(node.Chars[0]);
node = node_a;
}
return builder.ToString();
}
static bool[] encode(string text, out Node node)
{
char[] chars;
int[] counts;
calc(text, out chars, out counts);
sort(chars, counts);
node = tree(chars, counts);
bool[] encoded_text = new bool[0];
for (int i = 0; i < text.Length; i++)
{
bool[] code = calc_code(node, text[i]);
int length = encoded_text.Length;
Array.Resize<bool>(ref encoded_text, length + code.Length);
Array.Copy(code, 0, encoded_text, length, code.Length);
}
return encoded_text;
}
public void Build(string source)
{
foreach (Char t in source)
{
if (!Frequencies.ContainsKey(t))
{
Frequencies.Add(t, 0);
}
Frequencies[t]++;
}
Debug.Assert( Frequencies != null, "Frequencies != null" );
foreach (KeyValuePair<char, int> symbol in Frequencies)
nodes.Add( new Node() { Symbol = symbol.Key, Frequency = symbol.Value } );
while (nodes.Count > 1)
{
List<Node> orderedNodes = nodes.OrderBy(node => node.Frequency).ToList();
if (orderedNodes.Count >= 2)
{
// Take first two items
List<Node> taken = orderedNodes.Take(2).ToList();
// Create a parent node by combining the frequencies
Node parent = new Node
{
Frequency = taken[0].Frequency + taken[1].Frequency,
Left = taken[0],
Right = taken[1],
Symbol = '*'
};
nodes.Remove(taken[0]);
nodes.Remove(taken[1]);
nodes.Add(parent);
}
this.Root = nodes.FirstOrDefault();
}
}
static bool[] calc_code(Node node, char c)
{
bool[] code = new bool[0];
while (true)
{
if (node.IsEnd)
break;
Array.Resize<bool>(ref code, code.Length + 1);
if (node.A.Chars.Contains(c))
{
node = node.A;
code[code.Length - 1] = false;
}
else
{
node = node.B;
code[code.Length - 1] = true;
}
}
return code;
}
public Node(Node a, Node b)
{
this.a = a;
this.b = b;
this.value = a.Value + b.Value;
this.Chars = new char[a.Chars.Length + b.Chars.Length];
Array.Copy(a.Chars, 0, this.chars, 0, a.Chars.Length);
Array.Copy(b.Chars, 0, this.chars, a.Chars.Length, b.Chars.Length);
}
static Node tree(char[] chars, int[] counts)
{
Node[] nodes = new Node[chars.Length];
for (int i = 0; i < nodes.Length; i++)
nodes[i] = new Node(chars[i], counts[i]);
do
{
int a_index = min_node(nodes, -1);
int b_index = min_node(nodes, a_index);
Node c = new Node(nodes[a_index], nodes[b_index]);
nodes[a_index] = c;
nodes[b_index] = null;
int count = 0;
for (int i = 0; i < nodes.Length; i++)
if (nodes[i] != null)
count++;
if (count == 1)
break;
}
while (true);
Node node = null;
for (int i = 0; i < nodes.Length; i++)
if (nodes[i] != null)
{
node = nodes[i];
break;
}
return node;
}
static int min_node(Node[] nodes, int ignore)
{
Node node = null;
int index = 0;
for (int i = 0; i < nodes.Length; i++)
if (nodes[i] != null && i != ignore)
{
node = nodes[i];
index = i;
break;
}
for (int i = 0; i < nodes.Length; i++)
if (nodes[i] != null && i != ignore && nodes[i].Value < node.Value)
{
node = nodes[i];
index = i;
}
return index;
}
public bool IsLeaf(Node node)
{
return (node.Left == null && node.Right == null);
}
