day 20

1 files changed, 42 insertions, 0 deletions

diff --git a/20.py b/20.py
new file mode 100644
index 0000000..19c09c3
--- /dev/null
+++ b/20.py
@@ -0,0 +1,42 @@
+from utils import open_day
+
+bg = False
+img = dict()
+with open_day(20) as f:
+    first, rest = f.read().rstrip().split('\n\n')
+    alg = [c == '#' for c in first]
+    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
+
+def iter():
+    global bg, img
+    new = dict()
+    minx, maxx = float('inf'), float('-inf')
+    miny, maxy = float('inf'), float('-inf')
+    for p, v in img.items():
+        if not v: continue
+        x, y = p
+        minx, maxx = min(minx, x), max(maxx, x)
+        miny, maxy = min(miny, y), max(maxy, y)
+    for y in range(miny - 1, maxy + 2):
+        for x in range(minx - 1, maxx + 2):
+            new[(x, y)] = alg[bits_at(img, x, y)]
+    img = new
+    bg = not bg
+
+iter()
+iter()
+
+print(sum(img.values()))
+
+for _ in range(48): iter()
+
+print(sum(img.values()))