From 258e8a568baaa3112419a72ad19d0a8e8ec4774d Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 14 Dec 2020 09:53:44 +0100
Subject: [PATCH] 2020: d15: ex2: add solution

---
 2020/d14/ex2/ex2.py | 56 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100755 2020/d14/ex2/ex2.py

diff --git a/2020/d14/ex2/ex2.py b/2020/d14/ex2/ex2.py
new file mode 100755
index 0000000..55c254c
--- /dev/null
+++ b/2020/d14/ex2/ex2.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+import itertools
+import re
+import sys
+from dataclasses import dataclass
+from typing import Dict, Iterator, List
+
+
+@dataclass
+class Mask:
+    ones: int
+    zeros: int
+
+
+Memory = Dict[int, int]
+
+
+def gen_floats(xs: int) -> Iterator[int]:
+    x_positions = [i for i in range(36) if (1 << i) & xs]
+
+    return (
+        sum(1 << x_positions[i] for i, v in enumerate(val) if v == 1)
+        for val in itertools.product([0, 1], repeat=len(x_positions))
+    )
+
+
+def solve(raw: List[str]) -> int:
+    mask = Mask(
+        0,
+        (2 << 36) - 1,
+    )
+    mem_pattern = re.compile("mem\\[([0-9]+)\\] = ([0-9]+)")
+    mask_pattern = re.compile("mask = ([01X]+)")
+    mem: Memory = {}
+    for instr in raw:
+        if (mem_match := mem_pattern.match(instr)) is not None:
+            addr, val = int(mem_match.group(1)), int(mem_match.group(2))
+            addr |= mask.ones
+            xs = ~mask.ones & mask.zeros
+            addr &= ~xs  # Put floating bits to 0
+            for x in gen_floats(xs):
+                mem[addr | x] = val
+        elif (mask_match := mask_pattern.match(instr)) is not None:
+            ones = int(mask_match.group(1).replace("X", "0"), 2)
+            zeros = int(mask_match.group(1).replace("X", "1"), 2)
+            mask = Mask(ones, zeros)
+    return sum(mem.values())
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()