Reduce large maze to single width corridors This reduces the permutations for a x x x b x To one (two steps north) from four (two steps north; one east, two north, one west; one east, one north, one west, one north; and one north, one east, one north, one west). Longer corridors were worse! We would filter this in the "been here before via another path" but that's still a lot of lookups in lists, which is inefficient.