private Dictionary<char, LetterNode> _childNodes;

/// <summary>
        /// Initializes a new instance of the <see cref="LetterNode"/> class.
        /// </summary>
        public LetterNode()
        {
        }

/// <summary>
        /// Initializes a new instance of the <see cref="LetterNode"/> class.
        /// </summary>
        /// <param name="letter">The letter.</param>
        public LetterNode(char letter)
            : this()
        {
            Letter = letter;
        }

/// <summary>
        /// The node's child nodes
        /// </summary>
        public Dictionary<char, LetterNode> ChildNodes
        {
            get
            {
                if (this._childNodes == null)
                {
                    this._childNodes = new Dictionary<char, LetterNode>(InitialSpreadCapacity);
                }
                return this._childNodes;
            }
        }

/// <summary>
        /// Describe the node is end of the word.
        /// </summary>
        public bool IsEndOfWord
        {
            get;
            set;
        }

/// <summary>
        /// Gets or sets the letter.
        /// </summary>
        /// <value>The letter.</value>
        public char Letter
        {
            get;
            set;
        }

/// <summary>
        /// Gets or sets the parent of this node.
        /// </summary>
        /// <value>The parent.</value>
        public LetterNode Parent
        {
            get;
            set;
        }

/// <summary>
        /// Gets the word defined at this element.
        /// </summary>
        /// <value>The word ending here (if this is a word, or the empty string.</value>
        public string Word
        {
            get
            {
                if (IsEndOfWord)
                {
                    StringBuilder sb = new StringBuilder(20);
                    sb.Append(Letter);
                    var node = Parent;
                    while (node != null)
                    {
                        sb.Insert(0, node.Letter);
                        node = node.Parent;
                    }
                    return sb.ToString();
                }
                else
                {
                    return string.Empty;
                }
            }
        }

}