From 1ed8961019c389053bda3492efa55c649b546eaf Mon Sep 17 00:00:00 2001
From: Kees van Kempen <git@keesvankempen.nl>
Date: Thu, 19 Dec 2024 13:45:32 +0100
Subject: [PATCH] 2024(5): halfly fix it, still need to only sum those that
 were updated

---
 2024/5/puzzle1.py |  4 ++-
 2024/5/puzzle2.py | 69 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 2024/5/puzzle2.py

diff --git a/2024/5/puzzle1.py b/2024/5/puzzle1.py
index 90c496a..4492493 100644
--- a/2024/5/puzzle1.py
+++ b/2024/5/puzzle1.py
@@ -31,7 +31,7 @@ def load_input(filename="input"):
 
 	return rules, updates
 
-def is_update_legal(update, rules) -> bool:
+def is_update_legal(update, rules, print_offence=False) -> bool:
 	for rule in rules:
 		# Find indices of left hand side and right hand side
 		lhs, rhs = rule
@@ -41,6 +41,8 @@ def is_update_legal(update, rules) -> bool:
 		# This reminds me of limes inferior and limes superior.
 		# Thanks, Mueger.
 		if max(indices(update, lhs)) > min(indices(update, rhs)):
+			if print_offence:
+				print(f"Rule", rule, "offended by update", update)
 			return False
 	return True
 
diff --git a/2024/5/puzzle2.py b/2024/5/puzzle2.py
new file mode 100644
index 0000000..3fb7a0c
--- /dev/null
+++ b/2024/5/puzzle2.py
@@ -0,0 +1,69 @@
+from puzzle1 import *
+
+
+verbose = True
+
+def swap(lst, idx_a, idx_b):
+	temp = lst[idx_a]
+	lst[idx_a] = lst[idx_b]
+	lst[idx_b] = temp
+
+def fix_update(update, rules):
+	"""Fixes update according to rules by reference."""
+
+	# Allow the loop to be restared after a fix.
+	i = 0
+	update_free = True
+	while i < len(rules):
+		lhs, rhs = rules[i]
+		# NOTE: This is too verbose.
+		#if verbose:
+		#	print(i, rules[i], end=" ")
+
+		if not lhs in update or not rhs in update:
+			i += 1
+			if i == len(rules) and not update_free:
+				i = 0
+				update_free = True
+			# NOTE: This is a copied condition from below.
+			continue
+
+		idx_lhs, idx_rhs = update.index(lhs), update.index(rhs)
+		if idx_lhs > idx_rhs:
+			if verbose:
+				print(f"swapping as {lhs} < {rhs}")
+			swap(update, idx_lhs, idx_rhs)
+			update_free = False
+
+		i += 1
+		if i == len(rules) and not update_free:
+			if verbose:
+				print("resetting")
+			i = 0
+			update_free = True
+		elif i == len(rules):
+			print("stopping")
+
+if __name__ == "__main__":
+	rules, updates = load_input()
+
+	indices_legal = []
+	middle_sum = 0
+	# Let's assume numbers can only occur once (although the checker does not
+	# make this assumption), and every update CAN be fixed.
+	for idx, update in enumerate(updates):
+		print(f"{idx:5d}/{len(updates)}:", update)
+		fix_update(update, rules)
+		updates[idx] = update
+		if is_update_legal(update, rules):
+			if verbose:
+				print(update, " is legal")
+			indices_legal.append(idx)
+			middle_sum += middle_page_num(update)
+		else:
+			if True or verbose:		
+				print(update, " is illegal")
+
+	if verbose:
+		print(indices_legal)
+	print(f"The sum of middle page numbers of legal updates is {middle_sum}.")