day 13

1 files changed, 35 insertions, 0 deletions

diff --git a/13.py b/13.py
new file mode 100644
index 0000000..2538e53
--- /dev/null
+++ b/13.py
@@ -0,0 +1,35 @@
+# pyright: strict
+from collections.abc import Iterable
+from functools import cache
+from sys import stdin
+
+
+@cache
+def rocks_to_int(bits: Iterable[str]) -> int:
+    return sum(2**i for i, bit in enumerate(bits) if bit == "#")
+
+
+@cache
+def diff(nums: tuple[int], cut: int) -> int:
+    return sum(
+        (nums[a] ^ nums[b]).bit_count()
+        for a, b in zip(range(cut - 1, -1, -1), range(cut, len(nums)))
+    )
+
+
+def find_mirror(nums: tuple[int, ...], difference: int) -> int:
+    for n in range(1, len(nums)):
+        if diff(nums, n) == difference:
+            return n
+    return 0
+
+
+p1 = p2 = 0
+for pattern in stdin.read().rstrip("\n").split("\n\n"):
+    pattern = pattern.split("\n")
+    rows = tuple(map(rocks_to_int, pattern))
+    cols = tuple(map(rocks_to_int, zip(*pattern)))
+    p1 += find_mirror(cols, 0) or find_mirror(rows, 0) * 100
+    p2 += find_mirror(cols, 1) or find_mirror(rows, 1) * 100
+
+print(p1, p2, sep="\n")