C # implement Huffman encoding and decoding

For more information about the concept of Huffman, see the data structure book.

using System; using System.Collections; using System.Collections.Generic; using System.Linq; using System.Text; namespace StringCompresser {     public class Huffman     {         //char and its bitarray         public Dictionary<char, BitArray> HuffmanCode = null;         //Huffman tree         public Node[] HuffmanTree = null;         //huffman tree node         internal struct Node         {             internal char character;             internal int weight;             internal int parent;             internal int lchild;             internal int rchild;         }         public Huffman(char[] charArray, int[] weight)         {             if (weight == null || weight.Length == 0                  || charArray == null || charArray.Length == 0                 || weight.Length != charArray.Length)                 return;             HuffmanCode = new Dictionary<char, BitArray>();             //build huffman tree             int totalNodeNum = weight.Length * 2 - 1;             HuffmanTree = new Node[totalNodeNum + 1];             //initialize the first weight.Length nodes with wight.             //The 0 element is reserved for other purpose             for(int i = 0; i < weight.Length; i++)             {                 HuffmanTree[i + 1] = new Node {                                                  weight = weight[i],                                                  parent = 0,                                                  lchild = 0,                                                  rchild = 0,                                                  character= charArray[i]                                                };             }             for (int i = weight.Length + 1; i < HuffmanTree.Length; i++)             {                 //select two min weight from huffmanTree.parent is 0
                //This Algorithm only traverse array once                #region selection                 int? min1 = null;                 int? min2 = null;                 int min1Pos = 0;                 int min2Pos = 0;                 for (int j = 1; j < i; j++)                 {                     if (HuffmanTree[j].parent == 0)                     {                         if (min1 == null)                         {                             min1 = HuffmanTree[j].weight;                             min1Pos = j;                             continue;                         }                         if (min2 == null)                         {                             if (HuffmanTree[j].weight < min1.Value)                             {                                 min2 = min1;                                 min2Pos = min1Pos;                                 min1 = HuffmanTree[j].weight;                                 min1Pos = j;                             }                             else                             {                                 min2 = HuffmanTree[j].weight;                                 min2Pos = j;                             }                             continue;                         }                         if(min1 != null && min2 != null)                         {                             if (HuffmanTree[j].weight < min1)                             {                                 min2 = min1;                                 min2Pos = min1Pos;                                 min1 = HuffmanTree[j].weight;                                 min1Pos = j;                             }                             else if (HuffmanTree[j].weight < min2)                             {                                 min2 = HuffmanTree[j].weight;                                 min2Pos = j;                             }                         }                     }                 }                 #endregion                 HuffmanTree[min1Pos].parent = HuffmanTree[min2Pos].parent = i;                 HuffmanTree[i].lchild = min1Pos;                 HuffmanTree[i].rchild = min2Pos;                 HuffmanTree[i].weight = min1.Value + min2.Value;                             }             //Get huffman code                          int p = 0,c =0;             List<bool> values = null;             for (int i = 1; i <= weight.Length; i++)             {                 values = new List<bool>();                                  //one points to _current node, one point to _parent node                 for (c = i, p = HuffmanTree[c].parent; p != 0; c = p, p = HuffmanTree[p].parent)                 {                     if (HuffmanTree[p].lchild == c)//0                     {                         values.Add(false);                     }                     else//1                     {                         values.Add(true);                     }                 }                 values.Reverse();                 HuffmanCode.Add(charArray[i - 1], new BitArray(values.ToArray()));             }                     }         //Encode a string to bitarray         public BitArray Encode(string input)         {             if (string.IsNullOrEmpty(input))                 return null;             List<bool> list = new List<bool>();             foreach (char ch in input)             {                 BitArray ba = HuffmanCode[ch];                 foreach (bool b in ba)                 {                     list.Add(b);                 }             }             return new BitArray(list.ToArray());         }         //Decode a bitarray to a string         public string Decode(BitArray bitArray)         {             if (bitArray == null)                 return null;             string rtnString = string.Empty;             int ic = HuffmanTree.Length - 1;//Root             Node current = HuffmanTree[ic];             int i = 0;             while (i <= bitArray.Length - 1)             {                 while (current.lchild != 0 && current.rchild != 0)                 {                     current = bitArray[i++] ? HuffmanTree[current.rchild] : HuffmanTree[current.lchild];                 }                 rtnString = string.Concat(rtnString, current.character);                 current = HuffmanTree[ic];             }             return rtnString;         }                  //Get char from a char bitarray         private char GetCharacter(BitArray array)         {             int ic = HuffmanTree.Length - 1;//Root             Node c = HuffmanTree[ic];                          foreach (bool b in array)             {                 if (b)                 {                     ic = c.rchild;                 }                 else                 {                     ic = c.lchild;                 }                 c = HuffmanTree[ic];             }             return c.character;         }     } }