C# TrieTree介绍及实现方法

   public class TrieTree   
   {       
   TrieNode _root = null; 
   private TrieTree()    
   {          
   _root = new TrieNode(char.MaxValue,0); 
   charCount = 0;  
   }      
   static TrieTree _instance = null;
   public static TrieTree GetInstance()  
   {           
   if (_instance == null)       
   {            
   _instance = new TrieTree();      
   }          
   return _instance;  
   }       
   public TrieNode Root  
   {          
   get { return _root;
   }  
   }       
   public void AddWord(char ch)
   {          
TrieNode newnode=_root.AddChild(ch);  
newnode.IncreaseFrequency();          
newnode.WordEnded = true;     
}        int charCount;   
public void AddWord(string word)  
{         
if (word.Length == 1)    
{              
AddWord(word[0]);    
charCount++;      
}        
else   
{                
char[] chars=word.ToCharArray();    
TrieNode node = _root;          
charCount += chars.Length;     
for (int i = 0; i < chars.Length; i++) 
{                   
TrieNode newnode=node.AddChild(chars[i]);   
newnode.IncreaseFrequency();          
node = newnode;          
}          
node.WordEnded = true; 
}      
}      
public int GetFrequency(char ch)  
{          
TrieNode matchedNode = _root.Children.FirstOrDefault(n => n.Character == ch); 
if (matchedNode == null)     
{              
return 0;       
}          
return matchedNode.Frequency; 
}      
public int GetFrequency(string word)
{       
if (word.Length == 1)
{             
return GetFrequency(word[0]);
}           
else     
{           
char[] chars = word.ToCharArray();
TrieNode node = _root;       
for (int i = 0; i < chars.Length; i++)  
{                
if (node.Children == null)  
return 0;             
TrieNode matchednode = node.Children.FirstOrDefault(n => n.Character == chars[i]);
if (matchednode == null)         
{                     
return 0;        
}                 
node = matchednode;   
}             
if (node.WordEnded == true)       
return node.Frequency;      
else                  
return -1;          
}     
}  
}

   public class TrieNode   
   {      
   public TrieNode(char ch,int depth)
   {          
   this.Character=ch;
   this._depth=depth;
   }      
   public char Character;
   int _depth;       
   public int Depth  
   {           
   get{return _depth;
   }     
   }    
   TrieNode _parent=null;
   public TrieNode Parent    
   {         
   get {
   return _parent;
   }         
   set { _parent = value;
   }
   }      
   public bool WordEnded = false; 
   HashSet<TrieNode> _children=null; 
   public HashSet<TrieNode> Children
   {          
   get {
   return _children;
   }      
   }       
   public TrieNode GetChildNode(char ch)
   {           
   if (_children != null)   
   return _children.FirstOrDefault(n => n.Character == ch); 
   else              
   return null;     
   }      
   public TrieNode AddChild(char ch)
   {          
   TrieNode matchedNode=null;     
   if (_children != null)     
   {              
   matchedNode = _children.FirstOrDefault(n => n.Character == ch); 
   }          
   if (matchedNode != null)  
   //found the char in the list  
   {               
   //matchedNode.IncreaseFrequency();     
   return matchedNode;        
   }          
   else         
   { 
   //not found      
   TrieNode node = new TrieNode(ch, this.Depth + 1);    
   node.Parent = this;     
   //node.IncreaseFrequency();           
   if (_children == null)              
   _children = new HashSet<TrieNode>();  
   _children.Add(node);             
   return node;         
   }      
   }      
   int _frequency = 0;      
   public int Frequency   
   {        
   get { return _frequency;
   }       
   }      
   public void IncreaseFrequency()     
   {         
   _frequency++;  
   }     
   public string GetWord()
   {            
   TrieNode tmp=this;    
   string result = string.Empty; 
   while(tmp.Parent!=null) //until root node 
   {               
   result = tmp.Character + result;  
   tmp = tmp.Parent;    
   }           
   return result;    
   }       
   public override string ToString()
   {         
   return Convert.ToString(this.Character);
   }   
   }