From 7d0a611d99c1d3c6250a26382482698cc084964e Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tk@the-tk.com>
Date: Thu, 16 Dec 2021 10:37:48 +0000
Subject: day 16

---
 16.py | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 16.py

diff --git a/16.py b/16.py
new file mode 100644
index 0000000..b5ef399
--- /dev/null
+++ b/16.py
@@ -0,0 +1,66 @@
+from __future__ import annotations
+from utils import open_day
+from bitstring import BitStream
+from dataclasses import dataclass
+from functools import reduce
+from operator import mul, gt, lt, eq
+
+@dataclass
+class Packet:
+    version: int
+    tag: int
+    contents: list[Packet] | int
+
+with open_day(16) as f:
+    bits = BitStream(bytes.fromhex(f.read().rstrip()))
+
+def get_packet(bits):
+    version, tag = bits.readlist('2*uint:3')
+    if tag == 4:
+        value = 0
+        while True:
+            keep_going, nybble = bits.readlist('bool,uint:4')
+            value <<= 4
+            value |= nybble
+            if not keep_going: break
+        return Packet(version, tag, value)
+    ltid = bits.read('uint:1')
+    contents = []
+    if ltid == 0:
+        length = bits.read('uint:15')
+        start = bits.pos
+        while bits.pos - start < length:
+            contents.append(get_packet(bits))
+    else:
+        packets = bits.read('uint:11')
+        for _ in range(packets):
+            contents.append(get_packet(bits))
+    return Packet(version, tag, contents)
+
+def sum_versions(packet):
+    if packet.tag == 4:
+        return packet.version
+    return packet.version + sum(sum_versions(p) for p in packet.contents)
+
+def evaluate(packet):
+    def eval_all(p):
+        for q in p.contents:
+            yield evaluate(q)
+    def binary_op(p, op):
+        assert(len(p.contents) == 2)
+        return int(op(evaluate(p.contents[0]), evaluate(p.contents[1])))
+    actions = [
+        lambda p: sum(eval_all(p)),
+        lambda p: reduce(mul, eval_all(p), 1),
+        lambda p: min(eval_all(p)),
+        lambda p: max(eval_all(p)),
+        lambda p: p.contents,
+        lambda p: binary_op(p, gt),
+        lambda p: binary_op(p, lt),
+        lambda p: binary_op(p, eq),
+    ]
+    return actions[packet.tag](packet)
+
+packet = get_packet(bits)
+print(sum_versions(packet))
+print(evaluate(packet))
-- 
cgit v1.2.3-54-g00ecf