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);

        }

    }