From fa9375ef9a4ecb36b28cdffe70f2d48cf9bdb58f Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Tue, 9 Dec 2025 08:26:58 +0100
Subject: Day 9 2025

---
 2025/09/b.py | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 2025/09/b.py

(limited to '2025/09/b.py')

diff --git a/2025/09/b.py b/2025/09/b.py
new file mode 100644
index 0000000..ad0095b
--- /dev/null
+++ b/2025/09/b.py
@@ -0,0 +1,37 @@
+import fileinput
+
+with fileinput.input() as lines:
+	a = [tuple(int(x) for x in l[:-1].split(',')) for l in lines]
+
+# Check if the border is turning clockwise or counter-clockwise
+def dir(p, q):
+	return p[0]*q[1]-p[1]*q[0]
+t = 0
+for i in range(len(a)):
+	p, q, r = a[i%len(a)], a[(i+1)%len(a)], a[(i+2)%len(a)]
+	t += 1 if dir((q[0]-p[0],q[1]-p[1]), (r[0]-q[0],r[1]-q[1])) > 0 else -1
+
+def lbreaks(p, q, tl, br):
+	# Adjust for horizontal or vertical
+	(tt, z) = (t, 0) if p[0] == q[0] else (-t, 1)
+
+	if min(p[1-z], q[1-z]) >= br[1-z] or max(p[1-z], q[1-z]) <= tl[1-z]:
+		return False
+	if p[z] == tl[z]:
+		return tt * (q[1-z]-p[1-z]) > 0
+	if p[z] == br[z]:
+		return tt * (q[1-z]-p[1-z]) < 0
+
+	return p[z] > tl[z] and p[z] < br[z]
+
+def admissible(a, i, j):
+	tl = (min(a[i][0], a[j][0]), min(a[i][1], a[j][1]))
+	br = (max(a[i][0], a[j][0]), max(a[i][1], a[j][1]))
+	return not any(lbreaks(a[k], a[(k+1)%len(a)], tl, br) for k in range(len(a)))
+
+s = 0
+for i in range(len(a)):
+	for j in range(i+1, len(a)):
+		if admissible(a, i, j):
+			s = max(s, (abs(a[i][0]-a[j][0])+1)*(abs(a[i][1]-a[j][1])+1))
+print(s)
-- 
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