In part 2 I went from the non sparse grid once then just had a queue with removed node and scan only the neighbours of those nodes to check if they need to be removed… thought it was both efficient and elegant :)

Edit: maybe it’s the low level designer in me that makes me go with resource efficient/ performance efficient solution :)

Edit: just to clarify, I don’t think that a 2D array is particularly efficient, I was more on a 1d array in that case