4 files changed, 233 insertions(+), 0 deletions(-)

M README.md
A day20/Makefile
A day20/day20.lua
A day20/input.txt

@@ 23,6 23,7 @@ of the solutions 😄
 * [Day 16][day16]: OCaml
 * [Day 17][day17]: Raku
 * [Day 18][day18]: Clojure
+* [Day 20][day20]: Lua
 
    [day1]: https://git.sr.ht/~srpablo/advent_of_code_2021/tree/main/item/day1/day1.factor
    [day2]: https://git.sr.ht/~srpablo/advent_of_code_2021/tree/main/item/day2/day2.sml


@@ 42,4 43,5 @@ of the solutions 😄
    [day16]: https://git.sr.ht/~srpablo/advent_of_code_2021/tree/main/item/day16/day16.ml
    [day17]: https://git.sr.ht/~srpablo/advent_of_code_2021/tree/main/item/day17/day17.raku
    [day18]: https://git.sr.ht/~srpablo/advent_of_code_2021/tree/main/item/day18/day18/src/day18/core.clj
+   [day20]: https://git.sr.ht/~srpablo/advent_of_code_2021/tree/main/item/day20/day20.lua
    [aoc]: https://adventofcode.com/2021

@@ 0,0 1,3 @@
+
+run:
+	lua day20.lua

@@ 0,0 1,126 @@
+-- Game of life!
+--
+-- To support infinite sequences, we'll represent the boards as tables (dictionaries)
+-- instead of tables (list of lists) ;)
+local function key(i, j)
+  return tostring(i) .. "," .. tostring(j)
+end
+
+
+local function tableLength(t)
+  local count = 0
+  for _ in pairs(t) do count = count + 1 end
+  return count
+end
+
+
+local function parseInput(filename)
+  local i = 1
+  local imageEnchancementLookup = {}
+  local theField = {}
+  for line in io.lines(filename) do
+    if i == 1 then
+      local imageEnchancementAlgorithm = line
+      for j = 1, #imageEnchancementAlgorithm do
+        local char = imageEnchancementAlgorithm:sub(j, j)
+        imageEnchancementLookup[j] = (char == "#")
+      end
+      goto continue
+    end
+    if i == 2 then goto continue end
+
+    for j = 1, #line do
+      local c = line:sub(j,j)
+      local rowIndex = i - 3
+      local colIndex = j - 1
+      if c == "#" then
+        local thisKey = key(rowIndex, colIndex)
+        theField[thisKey] = {rowIndex, colIndex}
+      end
+    end
+    ::continue::
+    i = i + 1
+  end
+  return imageEnchancementLookup, theField
+end
+
+
+local function getMinAndMax(field)
+  local xMin, xMax, yMin, yMax = 10000, 0, 10000, 0
+  for _, table in pairs(field) do
+    local x, y = table[1], table[2]
+    if x < xMin then
+      xMin = x
+    elseif x > xMax then
+      xMax = x
+    elseif y < yMin then
+      yMin = y
+    elseif y > yMax then
+      yMax = y
+    end
+  end
+  return {
+    xMin = (xMin - 1),
+    xMax = (xMax + 1),
+    yMin = (yMin - 1),
+    yMax = (yMax + 1)
+  }
+end
+
+
+local function digitForNeighbors(x, y, board, bounds, voidIsOn)
+  local offsets = {{-1, -1}, {-1, 0}, {-1, 1},
+                   {0, -1},   {0, 0},  {0, 1},
+                   {1, -1},   {1, 0}, {1, 1}}
+  local digit = 0
+  local powers = 1
+  -- Loop backwards to build up the binary digit.
+  for i = #offsets, 1, -1 do
+    local offset = offsets[i]
+    local xOff = x + offset[1]
+    local yOff = y + offset[2]
+    local inXBounds = bounds.xMin < xOff and xOff < bounds.xMax
+    local inYBounds = bounds.yMin < yOff and yOff < bounds.yMax
+    local inBounds = inXBounds and inYBounds
+    if (inBounds and board[key(xOff, yOff)]) or
+       (not inBounds and voidIsOn) then
+        digit = digit + powers
+    end
+    powers = powers * 2
+  end
+
+  -- Need to increment it since we index on it, and Lua
+  -- indexes start at 1
+  return (digit + 1)
+end
+
+
+local function runCycle(lookup, field, voidIsOn)
+  local newField = {}
+  local bounds = getMinAndMax(field)
+  for x = bounds.xMin, bounds.xMax do
+    for y = bounds.yMin, bounds.yMax do
+      local lookupDigit = digitForNeighbors(x, y, field, bounds, voidIsOn)
+      if lookup[lookupDigit] then
+        newField[key(x,y)] = {x, y}
+      end
+    end
+  end
+
+  return newField
+end
+
+
+-- Rack'em
+local lookup, field = parseInput("input.txt")
+for i = 1, 50 do
+  local voidIsOn = false
+  if i % 2 == 0 and lookup[1] then
+    voidIsOn = true
+  end
+  field = runCycle(lookup, field, voidIsOn)
+  if i == 2 then
+    print("Part 1: " .. tableLength(field))
+  end
+end
+print("Part 2: " .. tableLength(field))

@@ 0,0 1,102 @@
+###..##....#....##...#.#.#...######.#.#.#.###.####.....#.##...###......###.......#.#.#...##.##...#.#####..#.#.#.###..####..#.#..#..#...###.####..#.###.#...#.#.#.#...#.....#####..#.##.#.#.#.#...####.#.#....##..######..###.####......#..#..#####.##.#.#.#.#.####...###.####..#.#.#..##...#..#..#..##..##..###..#..#####.##...#.#.....##.#..##.#...####.#...#..##.#.#....#..#....##.#.#.###.#..#.###.###.######.##.######...#..##..##.#.###..#.###..#..#.########.###.#.#.#.#..##.#.#.###.#.###.#.#.###...#..#.##....##.##.##..
+
+.....#...#.####...#####..##..#.##.######...###.##.#.#.#...#####.#.#........#.######.#.#.##..####..#.
+##.#...##...######...##..####..####..#...##.#..##.#.##.#.....##.##.#.##...#####..#..#....#.###...###
+..#.##...#..#.....#..##.##...###..##..##....##...#..####.#....#.#.##.#.#.#..#.#.##..##.##.###.##..##
+......##.##.#.#.#....#..##.###.##.#.###..###.###....#...##.####.#.####.###..#..##.#.###....#.#..#.#.
+#.#...##.######.#..###..#.....##....####.#..###.##.#...#.#.#.#..####..#.#....#.#........#.#..#...##.
+.#.#####..##..###########.#..##.#..#####.#.#.###..#..##.##.#.#...#..##.#####...#.......#....#....###
+..#..#.##.#..##...##.#.#...###.#...#..##.##..####.#.#........##.#....#..###...##.#.#####.#...#..#.#.
+.###...###.#..#.##.#.##..#.#####.#.#...#.###.#...###.#...#....##.#..#.#####..##.#.###.#.....#..#.#..
+###...##..###.##...#..##...##.##..##.#..#.####.#.#.##..##.#..#.......##.#....####.#.####..###..#...#
+.#.....#.#.####..#.##.##..#######.##.###.#...#..#.##..#....#..####.#.#....#.#..#.#....##..#####..#.#
+.#.#..#..##..#..##.#........#...###..###.#...#.#...##..###...#.####..#####.####..#..##.##.####...###
+##.#....##.#.#..#.##.##.#.#...#.##.#.#....##.#.##.#.#####..#.#....#.###..#.#....###......####.######
+##..###.#.#.##.###...#.#.......#.#.##..##..####...#.###.##.##.#.#..###.##..##.#......##.###.....##..
+.#########..##..##.##.#.##..#.#######.#.#..######..###...##....####.#......###.####.#.#..####.###..#
+....###.####..#.#.....#...#......##.##.###.#.#.###..#.###..#..###....#.##.#.##.#.#..###..#..##..#.##
+#..#.#..#.#..##..##.####....##..#..#.####.#.#.#..##.##...#.###.##...###.#####..####.####..#..#####.#
+..#.......##....#.##...#.##...####..##...#.##..#.....#.######..##.#.#..##.##..##..#...#####..#...#..
+....#.#.###.##..#..###..#.#..#.###.##....#..#.##.##..##.#.####..####....##..####.#.##.#.#.######..##
+#.##.####.#####..####..##..###.########.#.#.#...##..#..#.#..#..#..###.##...##....#.#.##.#####....##.
+#.#..#.#.#..#.#.#.....#..#..#.####.##########.###.#....##.#.###.#.##.....#....#..##.###.###.#...###.
+.##.###.######.....#####.......###.#######.#....#.##..##...#...###.##.##.#..####....##.#..#.##.#.#.#
+.####..#.##.#.#...#.....###.....##..###.#.#.#..####..##..#.#######.#.#.##.######.##...###...#.#..#..
+.##.#..#.#.##..#..##.#..#...#...##...###...#.#.####.#...###...#.#.....####......#.######..####.#.###
+##..#.###..###....##.####.###..#..#.##.####.#.#.##..###..#.#.#..#..######...####...#..##.##..##..#.#
+##.#...#######.####.#.##.##.#.##...#.#...#.##.####.#.##.#..#.###......##.#.#.#...###.#...##..##.###.
+..###.#.##.#.#....##.#.###....##.#....##.##.#...##.#.#...###..#.#........#####..#####...##..#.#...#.
+##.....#...#.#...#....####..#.####.#.#......##....#...####..#.##..####..#.#.####.##.##.#.##.#####.#.
+....######....#..###.###..#..#####.###....#.##...#...#.#..#.....#.#####.##...##..###.##.#..#.####.##
+.##..###.#.#.#####...###.##.###.#.##..##..#..#.##.##....##..##...##.####..#.####...##.##.##...#..#..
+#.#..#####.#.#####...#.#..#...#.#.###...##.#.######....##....##.#..#.##.##.###..##.##.#####.#...##.#
+#..###.###.#.#####.#..#......#.#.##.###..##.#...###..####.#..#####...##.####.#...##.#.###.##...###.#
+###.###..####.#.#....#...#..##...#.###..#..#####.###.#.#.#..#..#.##...###.#.#.####.#.###..##..##.##.
+.#.#..#.#.#..#....##.#....#...#..#.#....###.#.#......##..##..#..###......##.####.#########....##...#
+#.....#.....##..##..###.##.##..####....#..#.##.##.#..##.##.#..####..#....####.#.#...##.#.#.###.#.##.
+.#..##.###.##..#..##..#.#..####......#..###.##..##...##..#....###.#.#.....###.##.##..##....#.#.##...
+.#...##.....#####.###..#...#.#.#...........#.##.#.......#.####...###.##..#..##.#...#..#########...#.
+########.####.##.......#.##.###.##.#.####.#..##.##.#.###..##.####..#..##.#..#...#.###......##.##.###
+.#.##...#.#######.###.#.######.#..###.#..##.#..##.###..##.#.##....####...#..##..#....#.#.##.#.##.#.#
+...#.#.#..##..##.#..####....##....#..#.#.#.##.#..#.#..#...####......##.....#.#.#..##...#..#.#..#...#
+.#.#####.#.#.#####.#####....##..##....####..#.###.#...###.#.##.#.#..##.#......#.###..#####....#..##.
+.#.###..####..###.###...#...#.###.#.##.##.##...#.....##.##..##..######.#.##.#.######..#.#.#.......#.
+#.....##.#..#.....#.##.##..#.#.###..##.##.##.#..#.#...#.#...##.....#.##.#.####.#.##.##.#.##.#..#.#..
+.#.#...#.##.##.#.#...#......##.#....#####.###.###.######..#.##.#..#.#..####..####.###..#.#....#..#.#
+.##.#..####.#...####..#..##.##.###..#..######..##.####....#..#.##..###..##.##.......#.##..##..###..#
+#....##.#.#.#...#.#..#...##.#.........##.#######..####.##..##.#####.##.#....##..#.####..###.####.#..
+#####...#.###.####.##....##.####.#...###.##...#...#####..#...#.....###..#.#.#.##..#....#.#.#.#..###.
+...#.#..####..##..##..#.###.......#..#.#..#...##....#...##.##.####..#...#.#...##.#..#.#.##...#.#.###
+##.#.#...####.###..##...#...##.####.#..#..#.###.##..##..######.##.#.##.#.##.##.#...##...###.#.#.#.#.
+....#....#.#.#.....#..###...#.####.#..#.###..#######..#.#...####...#...##...#.#..##.#.#..##.####.###
+..##.#..#.....#.....#.##.#.#.##.#####.##....###.#.##.....##.#...###.#.#..#....#..#####.#.##.##.#.##.
+###..##.#.#..##.##.##..##.....###.#.#..#.##....#...##..###.##.#...#.#.#.####.#..####...#.##.###..#..
+#....#.##..##.#..##...#.#.##..#.#..#..##.#....#.##....####..........##.##.....######.##...#.......#.
+#..#.##.###..##.#..#..#....#.####.#.....###.###....##...##..#..##.#####..#.#..########..#...####.#.#
+###.#..##....###.#..##..###.##.#..#....####....#.#.....#.#.#######.###.#.#.##.######....#.#.#....##.
+...#.##.###.##...##.####..#.###.##..#.#.###..###..#..#....###.###....##.....#..##..#..#.............
+..#...###...#####.###.###.##.....###....#....###.###...#.#.#.#.##.#..#..####.#....#...#.#..#.##.####
+#####....#.....#...###..#.#....#..#.###..#.####........###.##.#........###.#.##...##..#..#.##.#....#
+.####.#..##.#.##.######.......#.#.#...#..#.#..#....#.##..#...#.#######....####.#..##.#..##..##.###..
+.#.##...#.##...#..#..#..###..#.#.......#.##..#.#..#.###..##.....#.#.#######.....##..#.##.#.###.#.##.
+..##.#...##.###.##.#.#......##..##...##...###.#.##..#...#.#.####...#..##.#..#.##..##....#.##....###.
+#..############.#.#..#.##.##..#...#.......##.##..#.#..#..###....####...###.#.###..####.#.#.#..#..##.
+.#..#...#.##.##.#.##..#.##.###.....#..##...#.##......#.....##.#.##.##....####...#....##..##.####.##.
+#.###...##..#.##.##.######.#######.##..####.#..#.###.#.##...#.......#.######....###.#....##.#.##.#..
+#.##.........###....####.###.#.###.#....#.##.##.#.###...#.###..#.##.####.#######.###.#.##.##....#..#
+##..#.##...##.#..###.#.##.#..##...#....###.###.#..#.##....#.###...#.#.#...#####..#....#..####.#.###.
+#.####.#..#.####.###.######.##..#.#...#.####..#...###.#...#.####.....###..#..#..#..###.#.##.###.#..#
+#.##.#.######.##.#.#.#.#.#....#...#...##.####.###.##.#..###....#........#...###.#.#..#.##..####..##.
+...####.#.#.#.###........#####.###...#..#.#.......#....#..##.#.#.##.###...######..###.#...#.##.##.##
+.#..#.####.#..#.#....##..###.##..##.####..###....#.#..######...######.##.#.#.#.##.#....#.......##..#
+...###..#####......#.###..#...#...#.##.###.##...#.....###########....##..##...#.#...#.....##.#..#.##
+#.........#.##.#.#....#......#..#.##.#..####...#..#.###.##.####...#..##.#.##.#.#.##.#.##...#.#.#.###
+.#.#..#....#......#.#.#.......#...#..#.#..##..#####.#.#.#####.....#..#####.#..#..##.#.#####..#.#...#
+...#.#..#.##...#.#..#.##.##.##..#..#####.....#.###...##.#..#..#.....###.#.##..#.####.###.#..#..###.#
+.#.########.#.###..#....#.#####...######.#####.#..#.#####.#....#.....###..#..###.###.#..####..#....#
+####.#.#.####.#.#..###.##.....#.####..##.#..#....#.####.###.##....#####.#.##.#.##.......#.#.#..#.#..
+######..##.#...#.#.#####..#....#..#...###..#.#..##....#..##.....######..###.##.#.#.####.#.#...#..###
+.##......########.#..#.####.....####.#.###....##..##..##..#.##.#..#.##.###....##.#.....#.#.#.##...#.
+###.#...#...##...#.####.###.###.#..#..#..#.###...#..####..####.#.#...##..#############.#..#......#.#
+#.##.#...#.######.####...#.#.#.#.#.######.#..####..#....##..###..#..#.###..#....##.##.#...####.#.#.#
+.....#.###.#...###..##.###.#.###.#....###....#..##.#.##..##.#####..##.######.#..##.##..#.#.##.#..#..
+##..##.......#..####..##.#..#..#.##.#.#...#.....#.###...#.#....#.....#...#.#.#...##..#####.#.#.....#
+..###...#.....##..#.#.##..#...######...#...##.#..#.####...#.#......##.####..#..#####.#.###...#..##..
+###.#.#.....#..#.#..##.###...##.###..#...###.#.#..####...##..#.###..###.#...##.####.......##.##.....
+##.#.#.#.#.......####.##..###.###..######..##.#...#..###..##.#..###.##....###..###.##....####.##..##
+.#..#####..#..###......##.#..##.......###.#.#......##.##.##.####.#..#####.#####.#.....#..#..#.#..#.#
+...##.#.####.#...##.####..##.######.####.###...##...#.#..#####.....##.##...#.########.#..##.#..#.###
+#.##..#.##........#.#.##..#####..##.....##.#.###..######.###.#.#.....##..#........#....#.##.##......
+##..#...#.####.#..####..###...#.#..#.....##.##.###...#.##.....#....#....####.#..####...#.###..#.#.#.
+###.#.###...#.######....###..#...#.#..#....####.#.####..#.#.#.##.###..#..##..#.###.##.##....####...#
+#.##.#.#...##.....##.#..##....######....######.#.##.#...##.#.......#...##..##..##..###..#....####.#.
+###.###..#.##.##.....#..#.#..###..###....#...####.#######.##.##.#..###.###.#.###.#.........####..##.
+..###...####..#.##..####.##...##...#.####..#...#..#..####.##.#..#.....##..####.......#.#...##..##..#
+###..#.#.##.#.#..###....##.###..##.#####....####...###.#.#..#.##.#...#..#######..#.#.#.##.###....###
+#....###...#....#...###.#.##.#....###...#####...#.#......#.##.##.#....###...#.#.#.#.#.#..###..#.####
+..###...#.######.#..#..##.#....#####..####..###.#...####..#.#.#....#..#..###.#.##.....######.#..#..#
+##...#.##.#.##.###.#.#.##.###..###.####.####...#.###.####.##......#.#..#.###..#......#.#.....#######
+.#.#..#..#..#.##...####...#...#.....##.#.##..###.##.##.#.#.##..#.##...###...###...##..####.#.###.#.#
+..#...##.#.#.#.#..#####.####.#...##...#.#..####.....#.##..#.....#.#####.##...###..###....#.##...#..#
+##...#...##.###.#.###...#..##..##.##..#.....##.###..#...##....###.#.##.#.#...###....#.##.###.####...
+###...##.###.##........####...#.......##..###.##..#..####....###.#.###...#...###.#.#.#.###........#.