/// <summary>
/// Finds all the locked sets (aka naked sets) of a given size in a region.
/// </summary>
/// <remarks>
/// A locked set is a set of n cells in a given region which contain n or fewer
/// candidates between them.
/// </remarks>
/// <param name="constraint">The region being examined.</param>
/// <param name="size">The size of the locked sets to find.</param>
/// <returns></returns>
public static IEnumerable <Cell[]> FindLockedSets(this ICellConstraint constraint, int size, bool hidden)
{
if (!constraint.Unique)
{
yield break;
}
var availableCells = constraint.Cells.Where(cell => !cell.HasDigit);
var cellCount = availableCells.Count();
if (hidden)
{
size = cellCount - size;
}
var cellsToConsider = availableCells.Where(cell => cell.Candidates.Count <= size);
var combinations = cellsToConsider.Combinations(size).ToList();
foreach (var combination in combinations)
{
var candidates = combination.SelectMany(c => c.Candidates).Distinct().ToList();
if (candidates.Count <= size)
{
yield return(combination.ToArray());
}
}
}
public Intersection(ICellConstraint region1, ICellConstraint region2)
{
Region1 = region1;
Region2 = region2;
}
/// <summary>
/// Gets the cells intersecting two regions.
/// </summary>
/// <param name="constraint"></param>
/// <param name="other"></param>
/// <returns></returns>
public static IEnumerable <Cell> GetIntersectingCells
(this ICellConstraint constraint, ICellConstraint other)
{
return(constraint.Cells.Intersect(other.Cells).ToList());
}
/// <summary>
/// Gets a value indicating whether a constraint is a region.
/// A region is a unique constraint whose size equals the one dimensional
/// size of the grid, and which will therefore contain all the possible numbers
/// in the grid.
/// </summary>
/// <param name="constraint"></param>
/// <returns></returns>
public static bool IsRegion(this ICellConstraint constraint)
=> constraint.Unique && constraint.Cells.Count == constraint.Grid.Size;
