From c88196ecae5e477bcc152da6d8b266e5cbace17c Mon Sep 17 00:00:00 2001
From: dece <shgck@pistache.land>
Date: Sat, 25 Dec 2021 17:10:05 +0100
Subject: [PATCH] Day 20

---
 2021/day20.py | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 2021/day20.py

diff --git a/2021/day20.py b/2021/day20.py
new file mode 100644
index 0000000..5dff5c4
--- /dev/null
+++ b/2021/day20.py
@@ -0,0 +1,38 @@
+from operator import itemgetter as ig
+
+with open("input20.txt") as f:
+    lines = [line.rstrip() for line in f]
+iea = lines[0]
+data = {
+    (x, y): c == "#"
+    for x, line in enumerate(lines[2:])
+    for y, c in enumerate(line)
+}
+
+
+def near(x, y):
+    return ((a, b) for a in range(x - 1, x + 2) for b in range(y - 1, y + 2))
+
+
+def enhance(image, unkv):
+    next_image = {}
+    xmin, ymin = min(image, key=ig(0))[0] - 1, min(image, key=ig(1))[1] - 1
+    xmax, ymax = max(image, key=ig(0))[0] + 1, max(image, key=ig(1))[1] + 1
+    for x in range(xmin, xmax + 1):
+        for y in range(ymin, ymax + 1):
+            v = 0
+            for nnp in near(x, y):
+                v = (v << 1) | int(image.get(nnp, unkv))
+            next_image[(x, y)] = iea[v] == "#"
+    return next_image
+
+
+def solve(num_steps):
+    image = data
+    for i in range(num_steps):
+        image = enhance(image, i % 2 == 1)
+    print(sum(image.values()))
+
+
+solve(2)
+solve(50)