// function iterates through the encoded string
// if s[i]=='1' then move to node->right
// if s[i]=='0' then move to node->left
// if leaf node append the node->data to our output string
public string Decode(HuffmanTreeNode root, string encodedStr)
{
string ans = "";
HuffmanTreeNode curr = root;
// loop encoded str
for (int i = 0; i < encodedStr.Length; i++)
{
if (encodedStr[i] == '0') // move to left
{
curr = curr.Left;
}
else
{
curr = curr.Right; // move to right
}
// reached leaf node
if (curr.Left == null && curr.Right == null)
{
ans += curr.Char;
curr = root;
}
}
return(ans);
}
public void CreateTree(Dictionary <char, int> charFreqs)
{
// queue for nodes will be kept in asc order
queue = new List <HuffmanTreeNode>();
// Huffman code table will be populated with chars and corresponding binaries counted from Huffman tree
CodeTable = new Dictionary <char, string>();
Console.WriteLine("\nHuffman tree:");
foreach (var item in charFreqs)
{
// create nodes based on chars and frequencies
HuffmanTreeNode node = new HuffmanTreeNode(item.Key, item.Value);
node.Left = null;
node.Right = null;
queue.Add(node);
}
HuffmanTreeNode root = null;
// queue handling
while (queue.Count > 1)
{
// 1st node with smallest frequency to extract
HuffmanTreeNode x = queue.First();
queue.RemoveAt(0);
// 2nd node with smallest frequency y to extract
HuffmanTreeNode y = queue.First();
queue.RemoveAt(0);
// new node, daddy for the two extracted nodes (sum of the 2 smallest)
HuffmanTreeNode f = new HuffmanTreeNode('*', x.Frequency + y.Frequency);
// 1st extracted node as left child
f.Left = x;
// 2nd extracted node as right child
f.Right = y;
// new node is now root node
root = f;
// new node to the queue
queue.Add(f);
// sort queue, has to be in asc order
queue.Sort();
// for decoding
RootNode = root;
}
StoreCodes(root, ""); // to dict
}
// tree traversal
public void StoreCodes(HuffmanTreeNode root, string s)
{
// base case; if the left and right are null then its a leaf node and store the code s generated by traversing the tree.
if (root.Left == null && root.Right == null && Char.IsLetter(root.Char))
{
// codetable char
if (!CodeTable.ContainsKey(root.Char))
{
CodeTable.Add(root.Char, s);
}
CodeTable[root.Char] = s;
Console.WriteLine("\t\t" + root.Char + ":" + s);
return;
}
// if we go to left then add "0" to the code., if we go to the right add "1" to the code.
// recursive calls for left and right sub-tree of the generated tree.
StoreCodes(root.Left, s + "0");
StoreCodes(root.Right, s + "1");
}
