From d43c2fe4ae91c630c2864d7bdc82c4a00da02ba9 Mon Sep 17 00:00:00 2001
From: dece <shgck@pistache.land>
Date: Tue, 15 Dec 2020 22:30:58 +0100
Subject: [PATCH] Day 14

---
 2020/day14.py | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 2020/day14.py

diff --git a/2020/day14.py b/2020/day14.py
new file mode 100644
index 0000000..82fd1d4
--- /dev/null
+++ b/2020/day14.py
@@ -0,0 +1,55 @@
+import re
+import sys
+from itertools import combinations_with_replacement
+
+
+def main():
+    lines = [line.rstrip() for line in sys.stdin]
+
+    # Part 1
+    int_len = 36
+    meme = {}
+    mem_re = re.compile(r"mem\[(\d+)\] = (\d+)")
+    for line in lines:
+        if line.startswith("mask"):
+            mask_str = line.split("=")[1].strip()
+        elif (match := mem_re.match(line)):
+            addr, value = map(int, match.groups())
+            meme[addr] = apply_mask_p1(mask_str, value)
+    print("Init sum:", sum(meme.values()))
+
+    # Part 2 - what a mess
+    meme = {}
+    for line in lines:
+        if line.startswith("mask"):
+            mask_str = line.split("=")[1].strip()
+            ow_mask = int(mask_str.replace("X", "0"), 2)
+            floats = [i for i in range(int_len) if mask_str[::-1][i] == "X"]
+        elif (match := mem_re.match(line)):
+            addr, value = map(int, match.groups())
+            for masked_addr in apply_mask_p2(ow_mask, floats, addr):
+                meme[masked_addr] = value
+    print("Init sum p2:", sum(meme.values()))
+
+
+def apply_mask_p1(mask, value):
+    value &= int(mask.replace("X", "1"), 2)
+    return value | int(mask.replace("X", "0"), 2)
+
+
+def apply_mask_p2(ow_mask, floats, value):
+    value |= ow_mask
+    for bitbuffer in range(2 ** len(floats)):
+        new_value = value
+        for i, f in enumerate(floats):
+            bitbuffer_pos = 1 << i
+            bit_pos = 1 << f
+            if bitbuffer & bitbuffer_pos != 0:
+                new_value |= bit_pos
+            else:
+                new_value &= ~bit_pos
+        yield new_value
+
+
+if __name__ == "__main__":
+    main()