From 965aba2b2101f7cd1958f0f4f44cf153d652e67e Mon Sep 17 00:00:00 2001
From: Heiko Ludwig <heiko@earl-grey.de>
Date: Sat, 7 Dec 2024 10:05:26 +0100
Subject: [PATCH] solve day 5 part 1

---
 day_05/program.py | 42 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/day_05/program.py b/day_05/program.py
index 50cef13..7000ac3 100755
--- a/day_05/program.py
+++ b/day_05/program.py
@@ -7,9 +7,47 @@ def get_lines(filename: str) -> list:
         return [line.strip() for line in file.readlines()]
 
 
+def get_rules_and_updates(lines: list) -> tuple:
+    rules = {}
+    updates = []
+    for line in lines:
+        if "|" in line:
+            a, b = line.split("|")
+            if rules.get(b):
+                rules[b].append(a)
+            else:
+                rules[b] = [a]
+        elif "," in line:
+            updates.append(line.split(","))
+    return rules, updates
+
+
+def check_validity(rules: dict, update: list) -> bool:
+    for position, page_number in enumerate(update):
+        if page_number not in rules:
+            continue
+        # if a number that is supposed to come earlier than our current page_number
+        # is included in the rest of the update, it breaks the rules
+        for earlier_number in rules[page_number]:
+            if earlier_number in update[position:]:
+                return False
+    return True
+
+
+def get_middle_page_sums(rules: dict, updates: list) -> int:
+    middle_page_sum = 0
+    for update in updates:
+        if check_validity(rules, update):
+            middle_page_sum += int(update[int(len(update) / 2)])
+    return middle_page_sum
+
+
 def main():
-    lines = get_lines("sample-input.txt")
-    # lines = get_lines("input.txt")
+    # lines = get_lines("sample-input.txt")
+    lines = get_lines("input.txt")
+
+    rules, updates = get_rules_and_updates(lines)
+    print("Part 1: The sum of valid middle pages is:", get_middle_page_sums(rules, updates))
 
 
 if __name__ == '__main__':