/// <summary>
/// This method searches the board for an empty slot and then
/// enumerates all of the numbers that can possibly fit in
/// that hole.
/// </summary>
/// <param name="Node">The current node</param>
/// <returns>
/// An array of TempStruct nodes that contain the Row and
/// Column of the empty slot along with the values that can go
/// in that empty slot.
/// </returns>
/// <remarks></remarks>
private ValidNumberList FindLegalValues(TreeNode Node)
{
int Row = -1;
int Col = -1;
// Find the next row and column that still contains a
// zero (has no value).
bool foundHole = false;
for (int i = 0; !foundHole && i < Node.Order; i++)
{
for (int j = 0; !foundHole && j < Node.Order; j++)
{
if (Node.Board[i, j] == 0)
{
Row = i;
Col = j;
foundHole = true;
}
}
}
if (!foundHole)
{
// The board is complete, no holes, mark it as complete
// and push it.
Node.Complete = true;
m_listener.putNode(Node);
return (null);
}
// Walk through all of the potential numbers from 1 to
// m_order that might be in this slot and see if it works.
// Any that do work are stored in validNumberList.
Stack validNumberStack = new Stack();
for (byte nextNum = 1; (nextNum <= m_order); nextNum++)
{
bool itFits = true;
// Is this number already in the current row?
for (int i = 0; itFits && i <= (Row - 1); i++)
{
if (Node.Board[i, Col] == nextNum)
{
itFits = false;
}
}
// Is this number already in the current column?
for (int j = 0; itFits && j <= (Col - 1); j++)
{
if (Node.Board[Row, j] == nextNum)
{
itFits = false;
}
}
if (itFits) // This Number can go in this space
{
validNumberStack.Push(nextNum);
}
}
if (validNumberStack.Count == 0)
return (null);
else
return (new ValidNumberList(Row, Col, validNumberStack));
}
private void killNode(TreeNode deadNode)
{
deadNode.Deadend = true;
// Remove this dead node if possible.
if (deadNode.PrevNode != null)
{
Debug.Assert(deadNode.PrevNode.NextNode == deadNode);
TreeNode prevNode = deadNode.PrevNode;
// Take deadNode out of the loop
prevNode.NextNode.PrevNode = deadNode.PrevNode;
prevNode.NextNode = deadNode.NextNode;
// Note that we can't clear deadNode.NextNode
// yet since the caller may still use it to move
// to the next node, but we can clear PrevNode.
deadNode.PrevNode = null;
// This object can be cleaned up as soon as the
// caller drops its reference.
}
else
{
// Since we are first in line, see if we can point
// our parent to our next node to get out of memory.
if (deadNode.Parent != null)
{
TreeNode ourParentNode = deadNode.Parent;
// If we are an only child deadend then our parent
// is a Deadend as well by definition
if (null == deadNode.NextNode)
{
deadNode.Parent = null;
ourParentNode.Son = null;
// Kill our parent too.
killNode(ourParentNode);
}
else
{
// Take deadNode out of the loop
ourParentNode.Son = deadNode.NextNode;
deadNode.NextNode.Parent = ourParentNode;
deadNode.NextNode.PrevNode = null;
}
}
}
}
/// <summary>
/// Instantiate a TreeNode using a source node for the board
/// and order. Does not copy the "tree" (Son and NextNode).
/// </summary>
/// <param name="sourceNode">The node to copy.</param>
public TreeNode(TreeNode sourceNode)
: this(sourceNode.m_order)
{
CopyBoard(sourceNode);
}
/// <summary>
/// This method tries to generate all possible children for a
/// ParentNode and generate their children recursively by
/// calling itself again on each child
/// </summary>
/// <param name="ParentNode">
/// Parent node - we will generate its possible children
/// </param>
/// <remarks></remarks>
private void GenerateTree(TreeNode ParentNode)
{
ValidNumberList LegalValueList = FindLegalValues(ParentNode);
if (null == LegalValueList)
{
// ParentNode is either a complete node or a dead end,
// either way it can now be removed from the tree
killNode(ParentNode);
return;
}
TreeNode CursorNode = new TreeNode(ParentNode);
CursorNode.SetAt(LegalValueList.Row,
LegalValueList.Col,
LegalValueList.Pop());
TreeNode Head = CursorNode;
// Loop through the children, skipping the first item (item
// zero) since we took care of it above.
while (LegalValueList.Count > 0)
{
// Create a new TreeNode for each possible value found
TreeNode TempNode = new TreeNode(ParentNode);
TempNode.SetAt(LegalValueList.Row,
LegalValueList.Col,
LegalValueList.Pop());
// Add it to the end of the chain
CursorNode.NextNode = TempNode;
TempNode.PrevNode = CursorNode;
CursorNode = TempNode;
}
ParentNode.Son = Head;
Head.Parent = ParentNode;
TreeNode AnotherNode = new TreeNode(m_order);
AnotherNode = Head;
while (null != AnotherNode)
{
GenerateTree(AnotherNode);
AnotherNode = AnotherNode.NextNode;
}
// Release nodes to free memory
Head = null;
AnotherNode = null;
ParentNode = null;
}
public void CopyBoard(TreeNode sourceNode)
{
Debug.Assert(sourceNode.m_order == m_order);
Array.Copy(sourceNode.m_board, m_board, (m_order * m_order));
}
