From 1cdb49fe5bab260c9e2ca565f0b03a9a8eecac16 Mon Sep 17 00:00:00 2001
From: Alex Karle <alex@alexkarle.com>
Date: Tue, 3 Dec 2024 02:44:10 +0100
Subject: [PATCH] 2024: Golf day 2 pt 2 a bit

I'm fairly convinced this is true in the general case?
---
 2024/02/2.py | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/2024/02/2.py b/2024/02/2.py
index 3fa3e47..54a27fd 100644
--- a/2024/02/2.py
+++ b/2024/02/2.py
@@ -1,38 +1,38 @@
 import sys
 
-def is_safe(report):
+def bad_level(report):
     delta = None
     prev = None
     safe = True
-    for n in report:
+    for i in range(len(report)):
+        n = report[i]
         if prev:
             d2 = n - prev
             if not delta:
                 delta = d2
             if abs(d2) > 3 or d2 == 0 or (delta and delta * d2 < 0):
-                safe = False
-                break
+                return i
         prev = n
-    return safe
+    return -1
 
 total = 0
 for l in sys.stdin:
     report = [int(x) for x in l.split()]
+    t = total
 
-    safe = is_safe(report)
-    if not safe:
-        # feels like there should be a faster method than brute forcing
-        # every combination? Escaping me right now.
-        # The catch is that in cases like 1 3 2 3 4, we want to drop
-        # the first 3, but it doesn't _look_ bad until we see the 2.
-        # When we see the bad 2, we would have to try to drop the 2
-        for i in range(len(report)):
-            subrep = [report[j] for j in range(len(report)) if j != i]
-            safe = is_safe(subrep)
-            if safe:
-                break
-
-    if safe:
+    bad = bad_level(report)
+    if bad == -1:
         total += 1
+    else:
+        # it could be that the bad index is any of:
+        #  - the result returned by bad_level (1 10 2 3) -- bad causes spike
+        #  - the index before that (bad - 1)  (10 1 2 3) -- prev bad causes spike
+        #  - the index before that (bad - 2)  (1  2 1 0) -- sign change
+        for i in [0, 1, 2]:
+            if bad - i >= 0:
+                subrep = [report[j] for j in range(len(report)) if j != bad - i]
+                if bad_level(subrep) == -1:
+                    total += 1
+                    break
 
 print(total)
--
libgit2 1.8.1