public static Board SolveSingleThreaded(Board b)
{
var nextOpen = b.NextEmpty();
if (nextOpen == null)
{
return b;
}
var taken = b.UsedNumbersInSpace(nextOpen);
var available = b.TotalSpaceValues
.Except(taken)
.ToList();
//.Shuffle();
if (available.Count == 0)
{
return null;
}
foreach (var possible in available)
{
var newBoard = b.Snapshot();
newBoard.Set(nextOpen, possible);
var next = SolveSingleThreaded(newBoard);
if (next != null)
{
return next;
}
}
return null;
}