aoc2021 day 20

local code
local grid = {}
for v in getinput():gmatch("[^\n]+") do
    if not code then
        code = v
    else
        local row = {}
        for c in v:gmatch(".") do
            row[#row+1] = c == "#" and 1 or 0
        end
        grid[#grid+1] = row
    end
end

local borders = 0
for i = 1, 50 do
    local newgrid = {}
    for y = 0, #grid+1 do
        newgrid[y+1] = {}
        for x = 0, #grid+1 do
            local b = 0
            for dy = -1, 1 do
                for dx = -1, 1 do
                    local v = grid[y+dy] and grid[y+dy][x+dx] or borders
                    b = b*2 + v
                end
            end
            newgrid[y+1][x+1] = code:sub(b+1, b+1) == "#" and 1 or 0
        end
    end
    grid = newgrid
    borders = 1 - borders
    if i == 2 or i == 50 then
        local c = 0
        for y, row in pairs(grid) do
            for x, v in pairs(row) do
                c = c + v
            end
        end
        print(c)
    end
end