day 17

2 files changed, 92 insertions, 0 deletions

diff --git a/20/README b/20/README
index 4d7a179..9539541 100644
--- a/20/README
+++ b/20/README
@@ -18,6 +18,7 @@ Day     Time            Ans     Time            Ans
  14    4.357 15018100062885   55.561  5724245857696
  15    0.363            232 10516.154       18929178
  16  156.622          18227   33.297  2355350878831
+ 17    8.053            295  209.633           1972
       -------                 -------
 tot    TBD   ms                TBD   ms
 
@@ -26,6 +27,7 @@ Stats:
 
       -------Part 1--------   -------Part 2--------
 Day       Time  Rank  Score       Time  Rank  Score
+ 17   00:17:45   416      0   00:21:34   386      0
  16   00:13:11   830      0   00:50:54  1318      0
  15   00:59:43  5655      0   01:17:06  4904      0
  14   00:43:31  4037      0   01:00:44  2402      0
diff --git a/20/py/d17.py b/20/py/d17.py
new file mode 100644
index 0000000..5ec1419
--- /dev/null
+++ b/20/py/d17.py
@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+import aoc20
+import sys
+import functools
+from collections import defaultdict
+
+
+@functools.cache
+def neighbours3(p):
+    res = set()
+    for dx in range(-1, 1+1):
+        for dy in range(-1, 1+1):
+            for dz in range(-1, 1+1):
+                if dx == dy == dz == 0:
+                    continue
+                res.add((p[0] + dx, p[1] + dy, p[2] + dz))
+    return res
+
+
+def pt1(_in):
+    active = set()
+    board = defaultdict(lambda: 0)
+    for y in range(len(_in)):
+        for x in range(len(_in[y])):
+            if _in[y][x] == "#":
+                active.add((x, y, 0))
+                for n in neighbours3((x, y, 0)):
+                    board[n] += 1
+
+    for _ in range(6):
+        new_board = defaultdict(lambda: 0)
+        new_active = set()
+        for p, deg in board.items():
+            if p in active and 2 <= deg <= 3:
+                new_active.add(p)
+                for n in neighbours3(p):
+                    new_board[n] += 1
+            elif p not in active and deg == 3:
+                new_active.add(p)
+                for n in neighbours3(p):
+                    new_board[n] += 1
+        board = new_board
+        active = new_active
+    return(len(active))
+
+
+@functools.cache
+def neighbours4(p):
+    res = set()
+    for dx in range(-1, 1+1):
+        for dy in range(-1, 1+1):
+            for dz in range(-1, 1+1):
+                for dw in range(-1, 1+1):
+                    if dx == dy == dz == dw == 0:
+                        continue
+                    res.add((p[0] + dx, p[1] + dy, p[2] + dz, p[3] + dw))
+    return res
+
+
+def pt2(_in):
+    active = set()
+    board = defaultdict(lambda: 0)
+    for y in range(len(_in)):
+        for x in range(len(_in[y])):
+            if _in[y][x] == "#":
+                active.add((x, y, 0, 0))
+                for n in neighbours4((x, y, 0, 0)):
+                    board[n] += 1
+
+    for _ in range(6):
+        new_board = defaultdict(lambda: 0)
+        new_active = set()
+        for p, deg in board.items():
+            if p in active and 2 <= deg <= 3:
+                new_active.add(p)
+                for n in neighbours4(p):
+                    new_board[n] += 1
+            elif p not in active and deg == 3:
+                new_active.add(p)
+                for n in neighbours4(p):
+                    new_board[n] += 1
+        board = new_board
+        active = new_active
+    return(len(active))
+
+
+if __name__ == "__main__":
+    input = aoc20.read_input(sys.argv[1:], 17)
+    print(pt1(input))
+    print(pt2(input))