day 20: cleanup

1 files changed, 6 insertions, 9 deletions

diff --git a/20.py b/20.py
index 19c09c3..707c2b0 100644
--- a/20.py
+++ b/20.py
@@ -5,16 +5,17 @@ img = dict()
 with open_day(20) as f:
     first, rest = f.read().rstrip().split('\n\n')
     alg = [c == '#' for c in first]
+    assert(len(alg) == 512)
     for y, line in enumerate(rest.split('\n')):
         for x, c in enumerate(line):
             img[(x, y)] = c == '#'
 
 def bits_at(img, x, y):
     bits = []
-    for dx, dy in ((-1, -1), (0, -1), (1, -1), (-1, 0), (0, 0), (1, 0), (-1, 1), (0, 1), (1, 1)):
-        bits.append(img.get((x + dx, y + dy), bg))
-    val = int(''.join('1' if b else '0' for b in bits), 2)
-    return val
+    for dy in range(-1, 2):
+        for dx in range(-1, 2):
+            bits.append(img.get((x + dx, y + dy), bg))
+    return sum(b * 2 ** i for i, b in enumerate(reversed(bits)))
 
 def iter():
     global bg, img
@@ -32,11 +33,7 @@ def iter():
     img = new
     bg = not bg
 
-iter()
-iter()
-
+for _ in range(2): iter()
 print(sum(img.values()))
-
 for _ in range(48): iter()
-
 print(sum(img.values()))