public static SudokuBoard SolveInternal(SudokuBoard sudokuBoard)
{
if (!sudokuBoard.IsValid())
{
return(null);
}
var cells = Enumerable.Range(0, NumberOfBoardCellsInSingleDirection)
.SelectMany(
vni =>
Enumerable.Range(0, NumberOfBoardCellsInSingleDirection)
.Select(hni => new Cell(hni, vni, sudokuBoard._numbers))).ToList();
Debug.Assert(cells.Count == NumberOfBoardCellsInSingleDirection * NumberOfBoardCellsInSingleDirection);
var rows = Enumerable.Range(0, NumberOfBoardCellsInSingleDirection).Select(rowIndex =>
{
var rowCells = cells.Where(c => c.VerticalIndex == rowIndex).ToList();
return(new SolutionRegion(rowCells));
}).ToList();
// TODO: rows and cols are mismatched, imporve just for readability
var columns = Enumerable.Range(0, NumberOfBoardCellsInSingleDirection).Select(columnIndex =>
{
var columnCells = cells.Where(c => c.HorizontalIndex == columnIndex).ToList();
return(new SolutionRegion(columnCells));
}).ToList();
var quadrants = Enumerable.Range(0, NumberOfQuadrantsInOneDirection).SelectMany(quadrantHorizontalIndex =>
Enumerable.Range(0, NumberOfQuadrantsInOneDirection)
.Select(
quadrantVerticalIndex =>
new
{
QuadrantHorizontalIndex = quadrantHorizontalIndex,
QuadrantVerticalIndex = quadrantVerticalIndex
})).Select(i =>
{
var quardantCells =
cells.Where(
c =>
c.HorizontalIndex >=
i.QuadrantHorizontalIndex * NumberOfQuadrantCellsInOneDirection &&
c.HorizontalIndex <
(i.QuadrantHorizontalIndex + 1) * NumberOfQuadrantCellsInOneDirection &&
c.VerticalIndex >=
i.QuadrantVerticalIndex * NumberOfQuadrantCellsInOneDirection &&
c.VerticalIndex <
(i.QuadrantVerticalIndex + 1) * NumberOfQuadrantCellsInOneDirection
).ToList();
return(new SolutionRegion(quardantCells));
}).ToList();
Debug.Assert(new[] { rows, columns, quadrants }.All(s => s.Count == NumberOfBoardCellsInSingleDirection));
var solutionRegions = rows.Concat(columns).Concat(quadrants).ToList();
var cellsToSolutionRegionsMap = cells.ToDictionary(c => c,
c => (IReadOnlyCollection <SolutionRegion>)solutionRegions.Where(r => r.Cells.Contains(c)).ToList());
Debug.Assert(cellsToSolutionRegionsMap.Values.All(s => s.Count == 3));
var cellsToProcess = cells.Where(c => !c.Number.HasValue).ToList();
var processedCellsBacktrackingInfos = new Stack <CellBacktractingInfo>();
while (true)
{
var currentCellToProcess =
cellsToProcess.OrderBy(c => GetCellPossibleValues(c, cellsToSolutionRegionsMap[c]).Count)
.FirstOrDefault();
if (currentCellToProcess == null)
{
return(sudokuBoard);
}
Debug.Assert(!currentCellToProcess.Number.HasValue);
var currentCellToProcessPossibleValues = GetCellPossibleValues(currentCellToProcess,
cellsToSolutionRegionsMap[currentCellToProcess]);
var currentCellToProcessBacktrackingInfo = new CellBacktractingInfo(currentCellToProcess,
currentCellToProcessPossibleValues);
do
{
var currentCellToProcessPossibleNumber =
currentCellToProcessBacktrackingInfo.GetNextPossibleNumber();
if (!currentCellToProcessPossibleNumber.HasValue)
{
currentCellToProcessBacktrackingInfo.Cell.Number = null;
if (!processedCellsBacktrackingInfos.Any())
{
return(null);
}
currentCellToProcessBacktrackingInfo = processedCellsBacktrackingInfos.Pop();
cellsToProcess.Add(currentCellToProcessBacktrackingInfo.Cell);
continue;
}
currentCellToProcessBacktrackingInfo.Cell.Number = currentCellToProcessPossibleNumber;
processedCellsBacktrackingInfos.Push(currentCellToProcessBacktrackingInfo);
cellsToProcess.Remove(currentCellToProcessBacktrackingInfo.Cell);
break;
} while (true);
}
}