From 89ffc53ee9f67e509452ea5ac4683d94a62d8c4a Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tk@the-tk.com>
Date: Sat, 18 Dec 2021 23:39:30 +0000
Subject: day 18: now less confusing

---
 18.py | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/18.py b/18.py
index 59c3f8a..4281c57 100644
--- a/18.py
+++ b/18.py
@@ -29,7 +29,7 @@ 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_explode(n, depth=0):
     def try_add(n, val, access, primary, secondary):
         if val == 0: return 0
         content = access(n)
@@ -39,19 +39,17 @@ def try_explode(n):
         val = try_add(content, val, primary, primary, secondary)
         val = try_add(content, val, secondary, primary, secondary)
         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
-            return Pair(car_val.car, try_add(n, car_val.cdr, cdr, car, cdr))
-        else:
-            cdr_val = descend(n.cdr, depth + 1)
-            if cdr_val is not None:
-                if depth == 3: n.cdr = 0
-                return Pair(try_add(n, cdr_val.car, car, cdr, car), cdr_val.cdr)
-    return descend(n)
+    if not is_pair(n): return None
+    if depth == 4: return n
+    car_val = try_explode(n.car, depth + 1)
+    if car_val is not None:
+        if depth == 3: n.car = 0
+        return Pair(car_val.car, try_add(n, car_val.cdr, cdr, car, cdr))
+    else:
+        cdr_val = try_explode(n.cdr, depth + 1)
+        if cdr_val is not None:
+            if depth == 3: n.cdr = 0
+            return Pair(try_add(n, cdr_val.car, car, cdr, car), cdr_val.cdr)
 
 tests = [
     ('[[[[[9,8],1],2],3],4]', '[[[[0,9],2],3],4]'),
-- 
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