private static SudokuPuzzle Backtracking(SudokuPuzzle puzzle)
{
if (puzzle.IsComplete)
{
return(puzzle);
}
if (_stopwatch.Elapsed.Minutes >= 5)
{
return(null);
}
var cell = puzzle.NextCell();
// Keep track of first three steps
if (Steps.Count < 3)
{
Steps.Add(new SudokuPuzzleStepModel
{
Degree = puzzle.GetDegree(cell),
DomainSize = cell.Domain.Count,
SelectedCol = cell.Col,
SelectedRow = cell.Row
});
}
foreach (var value in cell.Domain)
{
// Generate next node
var clone = puzzle.Clone();
clone.SetCellValue(cell.Row, cell.Col, value);
// If there exists a cell with an empty domain after forward checking, backtrack
if (clone.MinRemainingValue()?.Domain.Count == 0)
{
continue;
}
var result = Backtracking(clone);
if (result != null)
{
return(result);
}
}
return(null);
}
