From cd99a23d76b37eb7de8501416166acf67d201d64 Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Fri, 25 Dec 2020 15:34:24 +0100
Subject: Add day 17

---
 17/a.lua     | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 17/b.lua     | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 17/input.txt |   8 ++++
 3 files changed, 250 insertions(+)
 create mode 100644 17/a.lua
 create mode 100644 17/b.lua
 create mode 100644 17/input.txt

diff --git a/17/a.lua b/17/a.lua
new file mode 100644
index 0000000..60c1b18
--- /dev/null
+++ b/17/a.lua
@@ -0,0 +1,116 @@
+input = io.lines('input.txt')
+active = 0
+
+world = {}
+
+function copy(world)
+    new_world = {}
+    for x = -world.bounds[1], world.bounds[1] do
+        for y = -world.bounds[2], world.bounds[2] do
+            for z = -world.bounds[3], world.bounds[3] do
+                set(new_world, x, y, z, get(world, x, y, z))
+            end
+        end
+    end
+
+    new_world.bounds = {}
+    for i, b in pairs(world.bounds) do
+        new_world.bounds[i] = b
+    end
+
+    return new_world
+end
+
+function iterate(world, f)
+    for x = -world.bounds[1], world.bounds[1] do
+        for y = -world.bounds[2], world.bounds[2] do
+            for z = -world.bounds[3], world.bounds[3] do
+                f(x, y, z, get(world, x, y, z))
+            end
+        end
+    end
+end
+
+function set(world, x, y, z, value)
+    if not world[x] then
+        world[x] = {}
+    end
+    if not world[x][y] then
+        world[x][y] = {}
+    end
+    world[x][y][z] = value
+    return world
+end
+
+function get(world, x, y, z)
+    if not world[x] then
+        return '.'
+    elseif not world[x][y] then
+        return '.'
+    elseif not world[x][y][z] then
+        return '.'
+    else
+        return world[x][y][z]
+    end
+end
+
+function step_cell(world, x, y, z)
+    active = 0
+    for dx = -1, 1 do
+        for dy = -1, 1 do
+            for dz = -1, 1 do
+                if not (dx == 0 and dy == 0 and dz == 0) then
+                    if get(world, x+dx, y+dy, z+dz) == '#' then
+                        active = active + 1
+                    end
+                end
+            end
+        end
+    end
+    
+    if get(world, x, y, z) == '#' then
+        if active == 2 or active == 3 then
+            return '#'
+        else
+            return '.'
+        end
+    else
+        if active == 3 then
+            return '#'
+        else
+            return '.'
+        end
+    end
+end
+
+i = 0
+for line in input do
+    for j = 1, line:len() do
+       set(world, i, j, 0, line:sub(j, j))
+    end
+    i = i + 1
+end
+
+world.bounds = { i, i, 1 }
+
+function bump(bounds)
+    return { bounds[1]+1, bounds[2]+1, bounds[3]+1 }
+end
+
+for round = 1, 6 do
+    new_world = {}
+    new_world.bounds = bump(world.bounds)
+    iterate(new_world, function (x, y, z, value)
+        set(new_world, x, y, z, step_cell(world, x, y, z))
+    end)
+    world = copy(new_world)
+end
+
+count = 0
+iterate(world, function (x, y, z, value)
+    if value == '#' then
+        count = count  + 1
+    end
+end)
+
+print(count)
diff --git a/17/b.lua b/17/b.lua
new file mode 100644
index 0000000..75dfff4
--- /dev/null
+++ b/17/b.lua
@@ -0,0 +1,126 @@
+input = io.lines('input.txt')
+
+world = {}
+
+function copy(world)
+    new_world = {}
+    for x = -world.bounds[1], world.bounds[1] do
+        for y = -world.bounds[2], world.bounds[2] do
+            for z = -world.bounds[3], world.bounds[3] do
+                for w = -world.bounds[4], world.bounds[4] do
+                    set(new_world, x, y, z, w, get(world, x, y, z, w))
+                end
+            end
+        end
+    end
+
+    new_world.bounds = {}
+    for i, b in pairs(world.bounds) do
+        new_world.bounds[i] = b
+    end
+
+    return new_world
+end
+
+function iterate(world, f)
+    for x = -world.bounds[1], world.bounds[1] do
+        for y = -world.bounds[2], world.bounds[2] do
+            for z = -world.bounds[3], world.bounds[3] do
+                for w = -world.bounds[4], world.bounds[4] do
+                    f(x, y, z, w, get(world, x, y, z, w))
+                end
+            end
+        end
+    end
+end
+
+function set(world, x, y, z, w, value)
+    if not world[x] then
+        world[x] = {}
+    end
+    if not world[x][y] then
+        world[x][y] = {}
+    end
+    if not world[x][y][z] then
+        world[x][y][z] = {}
+    end
+    world[x][y][z][w] = value
+    return world
+end
+
+function get(world, x, y, z, w)
+    if not world[x] then
+        return '.'
+    elseif not world[x][y] then
+        return '.'
+    elseif not world[x][y][z] then
+        return '.'
+    elseif not world[x][y][z][w] then
+        return '.'
+    else
+        return world[x][y][z][w]
+    end
+end
+
+function step_cell(world, x, y, z, w)
+    active = 0
+    for dx = -1, 1 do
+        for dy = -1, 1 do
+            for dz = -1, 1 do
+                for dw = -1, 1 do
+                    if not (dx == 0 and dy == 0 and dz == 0 and dw == 0) then
+                        if get(world, x+dx, y+dy, z+dz, w+dw) == '#' then
+                            active = active + 1
+                        end
+                    end
+                end
+            end
+        end
+    end
+    
+    if get(world, x, y, z, w) == '#' then
+        if active == 2 or active == 3 then
+            return '#'
+        else
+            return '.'
+        end
+    else
+        if active == 3 then
+            return '#'
+        else
+            return '.'
+        end
+    end
+end
+
+i = 0
+for line in input do
+    for j = 1, line:len() do
+       set(world, i, j, 0, 0, line:sub(j, j))
+    end
+    i = i + 1
+end
+
+world.bounds = { i, i, 1, 1 }
+
+function bump(bounds)
+    return { bounds[1]+1, bounds[2]+1, bounds[3]+1, bounds[4]+1 }
+end
+
+for round = 1, 6 do
+    new_world = {}
+    new_world.bounds = bump(world.bounds)
+    iterate(new_world, function (x, y, z, w, value)
+        set(new_world, x, y, z, w, step_cell(world, x, y, z, w))
+    end)
+    world = copy(new_world)
+end
+
+count = 0
+iterate(world, function (x, y, z, w, value)
+    if value == '#' then
+        count = count  + 1
+    end
+end)
+
+print(count)
diff --git a/17/input.txt b/17/input.txt
new file mode 100644
index 0000000..78d38bb
--- /dev/null
+++ b/17/input.txt
@@ -0,0 +1,8 @@
+##.#...#
+#..##...
+....#..#
+....####
+#.#....#
+###.#.#.
+.#.#.#..
+.#.....#
-- 
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