private bool _TrySolve(SquareTracker <TPuzzle> tracker)
{
var puzzle = tracker.Puzzle;
if (puzzle.NumEmptySquares == 0)
{
return(true);
}
Coordinate c = tracker.GetBestCoordinateToGuess();
Span <int> possibleValues = stackalloc int[puzzle.Size];
int numPossible = tracker.PopulatePossibleValues(in c, possibleValues);
for (int i = 0; i < numPossible; ++i)
{
int possibleValue = possibleValues[i];
if (tracker.TrySet(in c, possibleValue))
{
if (_TrySolve(tracker))
{
return(true);
}
tracker.UnsetLast();
}
}
return(false);
}
/// <summary>
/// Constructs a solver for the given square tracker.
/// </summary>
/// <param name="tracker">A square tracker referencing the puzzle to solve.</param>
public PuzzleSolver(
IPuzzle puzzle,
PossibleValues possibleValues,
ISudokuRuleKeeper ruleKeeper,
ISudokuHeuristic?heuristic = null)
{
_tracker = new SquareTracker(puzzle, possibleValues, ruleKeeper, heuristic);
}
/// <inheritdoc/>
public bool TrySolve(TPuzzle puzzle, bool randomizeGuesses = false)
{
if (!SquareTracker <TPuzzle> .TryInit(puzzle, _ruleKeeper, _heuristic, out SquareTracker <TPuzzle>?tracker))
{
return(false);
}
return(randomizeGuesses ? _TrySolveRandomly(tracker !, new Random()) : _TrySolve(tracker !));
}
/// <summary>
/// Creates a deep copy of this ISquareTracker in its current state.
/// </summary>
public SquareTracker(SquareTracker existing)
{
_puzzle = existing._puzzle.DeepCopy();
_possibleValues = new PossibleValues(existing._possibleValues);
_ruleKeeper = existing._ruleKeeper.CopyWithNewReferences(_puzzle, _possibleValues);
_heuristic = existing._heuristic?.CopyWithNewReferences(
_puzzle, _possibleValues, _ruleKeeper.GetRules());
_setCoords = new Stack <Coordinate>(existing._setCoords);
_coordsThatUsedHeuristics = new Stack <Coordinate>(existing._coordsThatUsedHeuristics);
}
/// <summary>
/// Creates a deep copy of this tracker in its current state.
/// </summary>
internal SquareTracker(SquareTracker <TPuzzle> existing)
{
_puzzle = existing._puzzle.DeepCopy();
_setCoords = new Stack <Coordinate>(existing._setCoords);
if (existing._coordsThatUsedHeuristics is not null)
{
_coordsThatUsedHeuristics = new Stack <Coordinate>(existing._coordsThatUsedHeuristics !);
}
_ruleKeeper = existing._ruleKeeper.CopyWithNewReferences(_puzzle);
_heuristic = existing._heuristic?.CopyWithNewReferences(
_puzzle, _ruleKeeper.GetRules());
}
private SolveStats _ComputeStatsForAllSolutions(
TPuzzle puzzle, bool validateUniquenessOnly, CancellationToken?cancellationToken)
{
cancellationToken?.ThrowIfCancellationRequested();
// Copy the puzzle so that the given puzzle is not modified.
if (!SquareTracker <TPuzzle> .TryInit(puzzle.DeepCopy(), _ruleKeeper, _heuristic, out SquareTracker <TPuzzle>?tracker))
{
// No solutions.
return(new SolveStats());
}
return(_TryAllSolutions(tracker !, validateUniquenessOnly, cancellationToken));
}
private bool _TrySolveRandomly(SquareTracker <TPuzzle> tracker, Random random)
{
if (tracker.Puzzle.NumEmptySquares == 0)
{
return(true);
}
Coordinate c = tracker.GetBestCoordinateToGuess();
Span <int> possibleValues = stackalloc int[tracker.Puzzle.Size];
int numPossible = tracker.PopulatePossibleValues(in c, possibleValues);
while (numPossible > 0)
{
int possibleValue = Spans.PopRandom(random, possibleValues[0..numPossible--]);
/// <summary>
/// Tries to construct and initialize a tracker for the given puzzle, rules, and heuristics.
/// </summary>
/// <param name="puzzle">The puzzle to solve.</param>
/// <param name="ruleKeeper">The rule-keeper to satisfy.</param>
/// <param name="heuristic">An optional heuristic to user.</param>
/// <param name="tracker">
/// An <c>out</c> param where the tracker will be created. Set to null if initialization
/// fails (i.e. this method returns false).
/// </param>
/// <returns>
/// False if initialization fails, for example if the puzzle violates a rule, else true.
/// </returns>
internal static bool TryInit(
TPuzzle puzzle,
IRuleKeeper ruleKeeper,
IHeuristic?heuristic,
out SquareTracker <TPuzzle>?tracker)
{
if (!ruleKeeper.TryInit(puzzle) ||
(!heuristic?.TryInitFor(puzzle) ?? false))
{
tracker = null;
return(false);
}
tracker = new SquareTracker <TPuzzle>(puzzle, ruleKeeper, heuristic);
return(true);
}
private static SolveStats _TryAllSolutionsWithGuess(
SquareTracker tracker,
Coordinate c,
List <int> valuesToGuess)
{
var solveStats = new SolveStats();
for (int i = 0; i < valuesToGuess.Count - 1; i++)
{
var trackerCopy = new SquareTracker(tracker);
if (trackerCopy.TrySet(in c, valuesToGuess[i]))
{
SolveStats guessStats = _TryAllSolutions(trackerCopy);
solveStats.NumSolutionsFound += guessStats.NumSolutionsFound;
solveStats.NumSquaresGuessed += guessStats.NumSquaresGuessed;
solveStats.NumTotalGuesses += guessStats.NumTotalGuesses;
}
}
if (tracker.TrySet(in c, valuesToGuess[^ 1]))
private static SolveStats _TryAllSolutions(SquareTracker tracker)
{
if (tracker.Puzzle.NumEmptySquares == 0)
{
return(new SolveStats()
{
NumSolutionsFound = 1,
});
}
Coordinate c = tracker.GetBestCoordinateToGuess();
List <int>?possibleValues = tracker.GetPossibleValues(in c);
if (possibleValues.Count == 1)
{
if (tracker.TrySet(in c, possibleValues[0]))
{
return(_TryAllSolutions(tracker));
}
return(new SolveStats());
}
return(_TryAllSolutionsWithGuess(tracker, c, possibleValues));
}
/// <summary>
/// Constructs a solver for a standard Sudoku puzzle that uses a standard heuristic and
/// standard rule keeper. Provided for convenience.
/// </summary>
public PuzzleSolver(Puzzle puzzle)
{
_tracker = new SquareTracker(puzzle);
}