2025: improve folder names

2024/05/puzzle2.py

@@ -0,0 +1,50 @@
+from puzzle1 import *
+
+
+verbose = False
+
+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
+	swap_free = False
+	while not swap_free:
+		swap_free = True
+		for rule in rules:
+			lhs, rhs = rule
+
+			if not lhs in update or not rhs in update:
+				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)
+				swap_free = False
+
+if __name__ == "__main__":
+	rules, updates = load_input()
+
+	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):
+		if verbose:
+			print(f"{idx:5d}/{len(updates)}:", update)
+		if is_update_legal(update, rules):
+			if verbose:
+				print(update, " is legal")
+		else:
+			if verbose:
+				print(update, " is illegal")
+			fix_update(update, rules)
+			middle_sum += middle_page_num(update)
+
+	print(f"The sum of middle page numbers of legal updates is {middle_sum}.")