/// <summary>
/// Considers each cell of the grid.
/// </summary>
/// <returns>
/// Returns the cell with the smallest number
/// of possible values. This square is a good
/// place to continue search.
/// Returns null if the grid is invalid.
/// </returns>
private CellConsideration Consider(Grid grid)
{
int smallestNOfHints = int.MaxValue;
CellConsideration smallestConsideration = null;
for (int row = 0; row < 9; row++)
{
for (int col = 0; col < 9; col++)
{
if (grid.Get(row, col) == 0)
{
List <int> hints = GetHintsFor(grid, row, col);
if (hints.Count == 0)
{
// We found a square that has no solution
// This means the current state of the puzzle is bogus
// so stop.
return(null);
}
if (hints.Count < smallestNOfHints)
{
smallestConsideration = new CellConsideration(row, col, hints);
smallestNOfHints = hints.Count;
}
}
}
}
return(smallestConsideration);
}
/// <summary>
/// The actual meat of the depthfirst search goes here.
/// (solve is mostly bookkeeping)
/// </summary>
/// <param name="eachSolutionAction">
/// This lambda will be run once for each solution.
/// </param>
/// <param name="grid">
/// This grid will be left in an undefined state
/// after DepthFirstSearch() terminates.
/// If you want a good solution, be sure to save
/// a copy in your eachSolutionAction.
/// </param>
public void DepthFirstSearch(Grid grid, Action eachSolutionAction)
{
CellConsideration cell = Consider(grid);
if (grid.IsFull())
{
// Found a solution!
eachSolutionAction();
}
else if (cell != null)
{
foreach (int hint in cell.PossibleValues)
{
grid.Set(hint, true, cell.Row, cell.Col);
DepthFirstSearch(grid, eachSolutionAction);
grid.Set(0, true, cell.Row, cell.Col);
// speed hack: we know the previous square
// was a zero, so no need to save a copy
// of the grid every time.
}
}
}
/// <summary>
/// Considers each cell of the grid.
/// </summary>
/// <returns>
/// Returns the cell with the smallest number
/// of possible values. This square is a good
/// place to continue search.
/// Returns null if the grid is invalid.
/// </returns>
private CellConsideration Consider(Grid grid)
{
int smallestNOfHints = int.MaxValue;
CellConsideration smallestConsideration = null;
for (int row = 0; row < 9; row++)
{
for (int col = 0; col < 9; col++)
{
if (grid.Get(row, col) == 0)
{
List<int> hints = GetHintsFor(grid, row, col);
if (hints.Count == 0)
{
// We found a square that has no solution
// This means the current state of the puzzle is bogus
// so stop.
return null;
}
if (hints.Count < smallestNOfHints)
{
smallestConsideration = new CellConsideration(row, col, hints);
smallestNOfHints = hints.Count;
}
}
}
}
return smallestConsideration;
}
