C#实现TrieTree算法

   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;
            }
        }
    }

这里我们使用了单例模式，因为TrieTree类似缓存，不需要重复创建。下面是TreeNode的实现：

    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);
        }
    }