Help improve code efficiency

[ichabod801]

When you do Cnew[i][j] = 1, just append a tuple of the coordinates to you contaminated list: contaminated.append((i, j)). Then you loop through that list with for cx, xy in contaminated:.

Now, you'll have to do the check for the next set of cells in reverse. I would suggest a dictionary of tuples, reset each generation to empty. Ideally this would be a defaultdict, but you could just use get with a 0 default. So go through the neighbors of each contaminated space, and add one to the dictionary for the neighbor's coordinates. After all the contaminated squares are checked, loop through the dictionary and use the totals to check for new contaminations. Add those to your contaminated list.