2 files changed, 78 insertions, 0 deletions
diff --git a/2020/input/seventeen.txt b/2020/input/seventeen.txt
new file mode 100644
index 0000000..9511cae
--- /dev/null
+++ b/2020/input/seventeen.txt
@@ -0,0 +1,8 @@
+....###.
+#...####
+##.#.###
+..#.#...
+##.#.#.#
+#.######
+..#..#.#
+######.#
diff --git a/2020/seventeen.nim b/2020/seventeen.nim
new file mode 100644
index 0000000..70c1cd4
--- /dev/null
+++ b/2020/seventeen.nim
@@ -0,0 +1,70 @@
+# Day Seventeen: Conway Cubes
+import std/os, std/sets, std/enumerate
+
+let input: string = paramStr(1)
+type Coord = tuple[x,y,z: int]
+
+# Coordinate system: 0,0 is at the top left
+var dimension: HashSet[Coord]
+for y, line in enumerate(lines(input)):
+  for x, cube in line:
+    if cube == '#':
+      dimension.incl((x,y,0))
+      # stdout.write(x, ",", y, " ")
+    # stdout.write(cube)
+  # stdout.write('\n')
+# echo(dimension)
+
+## Return a tuple describing a dimension's largest axes
+func maximum(dim: HashSet[Coord]): tuple[x,y,z: int] =
+  result = (0,0,0)
+  for cube in dim:
+    if abs(cube.x) > result.x: result.x = abs(cube.x)
+    if abs(cube.y) > result.y: result.y = abs(cube.y)
+    if abs(cube.z) > result.z: result.z = abs(cube.z)
+
+## Return the number of cubes neighboring an arbitary point in space
+func neighbors(cube: Coord, dim: HashSet[Coord]): int =
+  result = 0
+  for x in -1 .. 1:
+    for y in -1 .. 1:
+      for z in -1 .. 1:
+        if ((cube.x+x, cube.y+y, cube.z+z) in dim) and ((x,y,z) != (0,0,0)):
+          inc(result)
+
+## Run one cycle of a pocket dimension
+func cycle(dim: HashSet[Coord]): HashSet[Coord] =
+  let max = maximum(dim)
+  for x in -max.x-1 .. max.x+1:
+    for y in -max.y-1 .. max.y+1:
+      for z in -max.z-1 .. max.z+1:
+        let coord = (x,y,z)
+        if coord in dim:
+          if coord.neighbors(dim) == 2 or coord.neighbors(dim) == 3:
+            result.incl(coord)
+        if coord notin dim:
+          if coord.neighbors(dim) == 3:
+            result.incl(coord)
+
+func cycle(dim: HashSet[Coord], reps: int): HashSet[Coord] =
+  result = dim
+  for i in 1 .. reps:
+    result = cycle(result)
+
+## Visualize output
+proc echo(dim: HashSet[Coord]) =
+  let max = maximum(dim)
+  for z in -max.z .. max.z:
+    stdout.write("z=", z, '\n')
+    for y in -max.y .. max.y:
+      for x in -max.x .. max.x:
+        if (x,y,z) == (0,0,0):
+          stdout.write('0')
+        elif (x,y,z) in dim:
+          stdout.write('#')
+        else:
+          stdout.write('.')
+      stdout.write('\n')
+    stdout.write('\n')
+
+echo len(dimension.cycle(6))