I just thought about this unfinished business.
I think the last remaining problem is to find the clusters of adjacent empty fields. (reminder: when you click an empty field - no mine and no adjacent mine - all adjacent empty fields are also revealed.)
There must be some math for that. Any ideas?
Probably a breadth-first graph algorithm leveraging the neighbours function for guiding the recursion.
Here’s a non-Elixir maze-finding example implementation that could maybe help? Just have to gloss over all the Rust type system discussions https://www.youtube.com/watch?v=FoNJ5zhL6bQ&t=3876s
This is what I came up with.
@board %{
0 => %{0 => 1, 1 => 1, 2 => 0, 3 => 0, 4 ...},
1 => %{0 => 9, 1 => 2, 2 => 2, 3 => 1, 4 ...},
...
}
def find_cluster(start, board),
do: _find_cluster([start], board, [start]) |> Enum.uniq()
def _find_cluster([h | t], board, found) do
found_ =
Minesweeper.neighbours(h)
|> Enum.filter(fn coord -> coord not in found end)
|> Enum.filter(fn {x, y} -> get_in(board, [y, x]) == 0 end)
_find_cluster(t, board, found) ++ _find_cluster(found_, board, found ++ found_)
end
def _find_cluster([], _board, found), do: found
I changed the print_board function so that it takes the cluster (found are marked a 8) and the startpoint (7). On the left the initial board with no clusters, empty cells are marked with 0.
start = {8, 0}
cluster = find_cluster(start, @board)
assert Minesweeper.print_board(Minesweeper.numbers(@mines), @mines, [], nil) ==
Minesweeper.print_board(Minesweeper.numbers(@mines), @mines, cluster, start)
FYI When dealing with multi dimensional arrays I normally just use a flat tuple key map. It saves you from a lot of head scratching issues.
indeed, would be simpler here. Getting rid of get_in for example. Also I don’t have the weird swap of x,y->y,x
So clear and clean in the end. 
I was also going to suggest a tuple key map for the found accumulator, or probably more ideal a MapSet.
Especially when dealing with a sparse, larger board the Enum.filter(fn coord -> coord not in found end) grows the search time non-linearly.
You could also drop the _find_cluster(t, board, found) ++ _find_cluster(found_, board, found ++ found_) in favour of just returning _find_cluster(found_, board, **updated found MapSet**), and set up the recursion with do: ([start] ++ _find_cluster([start], board, MapSet.new([start]))) |> Enum.uniq().
I probably missed some brackets
FYI My game initialization code is here mine_sweeper/lib/mine_sweeper/game_server.ex at bbaafba72905f1fffcd4dfc02432b07bffc0e549 · princemaple/mine_sweeper · GitHub
which I forgot to link to in the original post.
You’re right. I’ll do that as soon as I have at least 1000 paying customers playing at a time and keep it as simple as possible for now. 
I do not understand this part …? What should I do?
sorry for littering your thread, maybe this could be split …?
very very cool project and nice discussion. I’ll need to read up on Phoenix PubSub.broadcast to figure out what those calls are doing for you. Thanks for sharing this!
