static void IsolateSet(int set, Region region, SudokuModel model)
{
var cells = model.GetCells(region.Type, region.I);
var cellsNotContainedBySet = cells.Where(cell => (model.GetPossibilitySetCell(cell.Column, cell.Row) | set) != set).ToList();
var numCellsContainedBySet = cells.Length - cellsNotContainedBySet.Count;
if (numCellsContainedBySet != set.HiBitCount()) {
return;
}
// we now know that each of the numbers in the set must be exclusively in
// one of the contained cells, so we eliminate that set from all other cells'
// possibility bits.
var mask = ~set;
foreach (var cell in cellsNotContainedBySet) {
var poss = model.GetPossibilitySetCell(cell.Column, cell.Row);
model.SetPossibilitySetCell(cell.Column, cell.Row, poss & mask);
}
}