private List <HuffmanDicItem> CreateHuffmanDict(string code, HuffmanTreeNode current)
{
if (current == null)
{
throw new ArgumentNullException();
}
List <HuffmanDicItem> result = new List <HuffmanDicItem>();
if (current.LeftChild == null && current.RightChild == null)
{
result.Add(new HuffmanDicItem(current.Data, code));
}
else
{
List <HuffmanDicItem> dictL = CreateHuffmanDict(code + "0",
(HuffmanTreeNode)current.LeftChild);
List <HuffmanDicItem> dictR = CreateHuffmanDict(code + "1",
(HuffmanTreeNode)current.RightChild);
result.AddRange(dictL);
result.AddRange(dictR);
}
return(result);
}
private List <HuffmanDicItem> CreateHuffmanDict(HuffmanTreeNode root)
{
if (root == null)
{
throw new ArgumentNullException();
}
return(CreateHuffmanDict(string.Empty, root));
}
// 被外界调用的函数，对字符串进行huffman编码。
public string StringToHuffmanCode(out List <HuffmanDicItem> dict, string str)
{
List <HuffmanTreeNode> forest = CreateInitForest(str);
HuffmanTreeNode root = CreateHuffmanTree(forest);
dict = CreateHuffmanDict(root);
string result = ToHuffmanCode(str, dict);
return(result);
}
private List <HuffmanTreeNode> CreateInitForest(string str)
{
if (string.IsNullOrEmpty(str))
{
throw new ArgumentNullException();
}
List <HuffmanTreeNode> result = new List <HuffmanTreeNode>();
char[] charArray = str.ToCharArray();
List <IGrouping <char, char> > lst = charArray.GroupBy(a => a).ToList();
foreach (IGrouping <char, char> g in lst)
{
char data = g.Key;
int weight = g.ToList().Count;
HuffmanTreeNode node = new HuffmanTreeNode(data, weight);
result.Add(node);
}
return(result);
}
private HuffmanTreeNode CreateHuffmanTree(List <HuffmanTreeNode> sources)
{
if (sources == null)
{
throw new ArgumentNullException();
}
if (sources.Count < 2)
{
throw new ArgumentException("构造Huffman树，最少为2个结点。");
}
HuffmanTreeNode root = default(HuffmanTreeNode);
bool isNext = true;
while (isNext)
{
List <HuffmanTreeNode> lst = sources.OrderBy(a => a.Weight).ToList();
HuffmanTreeNode n1 = lst[0];
HuffmanTreeNode n2 = lst[1];
int weight = n1.Weight + n2.Weight;
HuffmanTreeNode node = new HuffmanTreeNode(weight);
node.LeftChild = n1;
node.RightChild = n2;
if (lst.Count == 2)
{
root = node;
isNext = false;
}
else
{
sources = lst.GetRange(2, lst.Count - 2);
sources.Add(node);
}
}
return(root);
}
