From ba48f135e0b52364c1ac765b227a06b8921a36c1 Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tk@the-tk.com>
Date: Sat, 18 Dec 2021 23:09:47 +0000
Subject: day 18: awful

---
 18.py | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 18.py

(limited to '18.py')

diff --git a/18.py b/18.py
new file mode 100644
index 0000000..57d06ce
--- /dev/null
+++ b/18.py
@@ -0,0 +1,103 @@
+from __future__ import annotations
+from copy import deepcopy
+from dataclasses import dataclass
+from functools import reduce
+from itertools import combinations
+from math import floor, ceil
+from utils import open_day
+
+@dataclass
+class Pair:
+    car: int | Pair
+    cdr: int | Pair
+    def __repr__(self) -> str:
+        return f'[{self.car},{self.cdr}]'
+
+def car(p, assign=None):
+    if assign is not None:
+        p.car = assign
+    return p.car
+def cdr(p, assign=None):
+    if assign is not None:
+        p.cdr = assign
+    return p.cdr
+
+def is_pair(p): return isinstance(p, Pair)
+
+def parse(s): return eval(s.replace('[', 'Pair(').replace(']', ')'))
+
+with open_day(18) as f:
+    homework = [parse(l) for l in f]
+
+def try_explode(n):
+    def try_add(n, val, primary, secondary):
+        if val == 0: return 0
+        if is_pair(primary(n)):
+            val = try_add(primary(n), val, primary, secondary)
+        else:
+            primary(n, primary(n) + val)
+            return 0
+        if val != 0:
+            if is_pair(secondary(n)):
+                val = try_add(secondary(n), val, primary, secondary)
+            else:
+                secondary(n, secondary(n) + val)
+                return 0
+        return val
+    def descend(n, depth=0):
+        if not is_pair(n): return None
+        if depth == 4: return n
+        car_val = descend(n.car, depth + 1)
+        if car_val is not None:
+            if depth == 3: n.car = 0
+            if not is_pair(n.cdr):
+                n.cdr += car_val.cdr
+                car_val.cdr = 0
+            return Pair(car_val.car, try_add(n.cdr, car_val.cdr, car, cdr))
+        else:
+            cdr_val = descend(n.cdr, depth + 1)
+            if cdr_val is not None:
+                if depth == 3: n.cdr = 0
+                if not is_pair(n.car):
+                    n.car += cdr_val.car
+                    cdr_val.car = 0
+                return Pair(try_add(n.car, cdr_val.car, cdr, car), cdr_val.cdr)
+    return descend(n)
+
+tests = [
+    ('[[[[[9,8],1],2],3],4]', '[[[[0,9],2],3],4]'),
+    ('[7,[6,[5,[4,[3,2]]]]]', '[7,[6,[5,[7,0]]]]'),
+    ('[[6,[5,[4,[3,2]]]],1]', '[[6,[5,[7,0]]],3]'),
+    ('[[3,[2,[1,[7,3]]]],[6,[5,[4,[3,2]]]]]', '[[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]]'),
+    ('[[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]]', '[[3,[2,[8,0]]],[9,[5,[7,0]]]]'),
+]
+
+for test, expect in tests:
+    test = parse(test)
+    try_explode(test)
+    assert(test == parse(expect))
+
+def try_split(n, access=lambda n: n):
+    content = access(n)
+    if is_pair(content):
+        return try_split(content, car) or try_split(content, cdr)
+    if content < 10: return False
+    content /= 2
+    access(n, Pair(floor(content), ceil(content)))
+    return True
+
+def reduce_num(n):
+    n = deepcopy(n)
+    while True:
+        if try_explode(n): continue
+        if try_split(n): continue
+        break
+    return n
+
+def magnitude(n):
+    if is_pair(n):
+        return 3 * magnitude(n.car) + 2 * magnitude(n.cdr)
+    return n
+
+print(magnitude(reduce(lambda a, b: reduce_num(Pair(a, b)), homework)))
+print(max(max(magnitude(reduce_num(Pair(a, b))), magnitude(reduce_num(Pair(b, a)))) for a, b in combinations(homework, 2)))
-- 
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