private static IReadOnlySet <Point> FlipTiles(IReadOnlySet <Point> tiles)
{
var newTiles = new HashSet <Point>();
var neighbours = CalculateNeighbours(tiles);
foreach (var tile in tiles)
{
var allNeighbours = neighbours[tile];
var activeNeighbours = allNeighbours.Intersect(tiles).Count();
if (activeNeighbours != 0 && activeNeighbours <= 2)
{
newTiles.Add(tile);
}
}
foreach (var tile in neighbours.SelectMany(x => x.Value).Distinct().Except(tiles))
{
if (tiles.Count(tile.IsNeighbour) == 2)
{
newTiles.Add(tile);
}
}
return(newTiles);
}
