Range scanning

function character.ValidTiles(start, mapModel, range)
    local found, following, current = {}, {[start] = 0}
    for step=1,range do
        current, following = following, {}
        for space in pairs(current) do
            if space.isTraversable then
                for neighbor in neighborsInMap(space) do
                    found[neighbor.yTile] = found[neighbor.yTile] or {}
                    if not found[neighbor.yTile][neighbor.xTile] then
                        found[neighbor.yTile][neighbor.xTile] = neighbor
                        following[neighbor] = step
                    end
                end
            end
        end
    end
    return found
end