/// <summary>
/// Find the node matching the string, if any.
/// </summary>
/// <param name="string"> The string to look for. </param>
public virtual LetterNode TerminalNode(string @string)
{
char key = Convert.ToChar(@string[0]);
LetterNode startNode = null;
if (!_words.ContainsKey(key))
{
return(null);
}
else
{
startNode = _words[key];
}
LetterNode node = startNode;
for (int i = 1; i < @string.Length; i++)
{
node = node.Child(@string[i]);
if (node == null)
{
break;
}
}
return(node);
}
/// <summary>
/// Find a forced win, if available. A forced win occurs from a
/// particular node when the all of the Children of a child node are either
/// terminals or forced wins.
/// </summary>
/// <param name="node"> The node from which to find a forced win. </param>
public virtual LetterNode ForcedWin(LetterNode node)
{
LetterNode winningChild = null;
foreach (LetterNode child in node.Children().Values)
{
if (!child.LeafNode)
{
winningChild = child;
foreach (LetterNode grandChild in child.Children().Values)
{
if (!(grandChild.LeafNode || (ForcedWin(grandChild) != null)))
{
winningChild = null;
break;
}
}
}
if (winningChild != null)
{
break;
}
}
return(winningChild);
}
/// <summary>
/// Determine if the string is the start of a word in the dictionary.
/// </summary>
/// <param name="stem"> The substring to look for. </param>
public virtual bool IsWordStem(string stem)
{
bool isWordStem = false;
LetterNode node = TerminalNode(stem);
if (node != null)
{
isWordStem = true;
}
return(isWordStem);
}
/// <summary>
/// Determine if the word is in the dictionary.
/// </summary>
/// <param name="word"> The word to look for. </param>
public virtual bool IsFullWord(string word)
{
bool isFullWord = false;
LetterNode node = TerminalNode(word);
if ((node != null) && (node.LeafNode))
{
isFullWord = true;
}
return(isFullWord);
}
/// <summary>
/// Find the longest word reachable from the specified node.
/// </summary>
/// <param name="node"> The node from which to find the longest word. </param>
public virtual LetterNode LongestWord(LetterNode node)
{
LetterNode longestChild = null;
foreach (LetterNode child in node.Children().Values)
{
if ((longestChild == null) || (child.MaxLength() > longestChild.MaxLength()))
{
longestChild = child;
}
}
return(longestChild);
}
/// <summary>
/// A test harness for the LetterNode class.
/// </summary>
/// <param name="args"> The command line arguments passed in. </param>
public static void TestLetterNode(string[] args)
{
if (args.Length > 0)
{
LetterNode node = new LetterNode(args[0]);
for (int i = 1; i < args.Length; i++)
{
node.AddWord(args[i]);
}
Console.Write("Total words = " + node.LeafNodeCount());
Console.Write("Maximum word length = " + node.MaxLength());
}
else
{
Console.Write("Usage: GhostGame " + typeof(LetterNode).FullName + " <word-list>");
}
}
/// <summary>
/// Get the player's next letter. This method is inherited from
/// GhostPlayer.
/// </summary>
/// <param name="wordInPlay"> The word currently being played. </param>
public virtual char Play(string wordInPlay)
{
char nextLetter = 'x';
LetterNode node = _dictionary.TerminalNode(wordInPlay);
if (node != null)
{
LetterNode forcedWin = ForcedWin(node);
if (forcedWin != null)
{
nextLetter = forcedWin.Letter();
}
else
{
nextLetter = LongestWord(node).Letter();
}
}
return(nextLetter);
}
/// <summary>
/// Add a word to the dictionary if it meets two criteria:
/// <ul>
/// <li> The word must be at least MIN_WORD_LENGTH letters long.
/// <li> The word must not start with another valid word.
/// </ul>
/// The second criteria is enforced by the LetterNode class.
/// </summary>
/// <param name="word"> The word to add to the dictionary. </param>
private void AddWord(string word)
{
if (word.Length >= MIN_WORD_LENGTH)
{
char key = Convert.ToChar(word[0]);
LetterNode node = null;
if (_words.ContainsKey(key))
{
node = _words[key];
}
if (node == null)
{
_words[key] = new LetterNode(word);
}
else
{
node.AddWord(word);
}
}
}
/// <summary>
/// Add a word to the tree rooted at this node. This method implements
/// the Ghost rule that no word may begin with another word. That
/// requires two rules:
///
/// - If this node has no child nodes, the passed word begins with
/// this word and must not be added.
/// - If the passed word has a length of zero, this is the end of the
/// word and all child nodes must be deleted.
/// </summary>
/// <param name="word"> The word, or substring, to add to this node. </param>
public void AddWord(string word)
{
if (word[0] == _letter)
{
if (_nodes.Count > 0)
{
if (word.Length == 1)
{
_nodes.Clear();
}
else
{
char key = Convert.ToChar(word[1]);
LetterNode nextNode = null;
if (_nodes.ContainsKey(key))
{
nextNode = _nodes[key];
}
if (nextNode == null)
{
_nodes[key] = new LetterNode(word.Substring(1));
}
else
{
nextNode.AddWord(word.Substring(1));
}
}
}
}
else
{
throw new ArgumentException("Invalid first letter.");
}
}
