public void Apply(MutablePuzzle puzzle, RegionQueue changedRegions)
{
if (++depth > 10)
{
return;
}
while (changedRegions.TryDequeue(puzzle, out var region))
{
for (int i = 0; i < Puzzle.LineLength; i++)
{
var value = region[i];
var coords = region.GetCoordinate(i);
if (value.GetOptionCount() != 2)
{
continue;
}
// if there are are only 2 bits set, bitwise and
// with the value - 1 will return the highest option
var highestValue = new SudokuValues(value.Values & (value.Values - 1));
#if DEBUG
Program.Debugger.AddAction($"Attempting {highestValue.Invert().Intersect(value)} in {coords}");
#endif
var oldSolver = _solver;
var changeset = new SingleCellChangeSet(new CellUpdate(highestValue, coords));
var newSolver = new Solver(changeset, _solver);
_solver = newSolver;
var(result, _) = newSolver.Solve();
_solver = oldSolver;
#if DEBUG
Program.Debugger.AddAction($"Result: {result}");
#endif
switch (result)
{
case SolveResult.Success:
puzzle.Absorb(newSolver.Puzzle);
return;
case SolveResult.Invalid:
// we picked the wrong digit
puzzle.RemoveOptions(new CellUpdate(highestValue.Invert(), coords));
return;
}
}
}
}
public void Apply(MutablePuzzle puzzle, RegionQueue changedRegions)
{
// keep scanning regions for naked singles, removing
// options when digits are placed. when a digit is placed,
// its box, row and column are added back to 'regions' so
// they can be scanned again.
while (changedRegions.TryDequeue(puzzle.Puzzle, out var region))
{
ScanRegion(changedRegions, puzzle, region);
}
}