BFS for finding frontiers is very slow when there are large unvisited areas

[Raghav-B]

This will also help remove any unnecessary backtracking

[Raghav-B]

Literally needed 4 lines of code. Untested, but should work :s

[Raghav-B]

Make it so that only tiles that are adjacent to a non-black tile are considered. Searching through the entire black mass is too time consuming.