Implement day 5

Author: sohrak

s5.py

@@ -21,20 +21,83 @@ def get_print_instructions():
     return ordering, updates
 
 
+def is_update_ordered(update, ordering):
+    for i in range(len(update)):
+        for j in range(i + 1, len(update)):
+            page1 = update[i]
+            page2 = update[j]
+            if page2 in ordering and page1 in ordering[page2]:
+                return False
+    return True
+
+
+def topological_sort(update, ordering):
+    """
+    Performs a topological sort on the given update based on the ordering rules.
+
+    Args:
+        update: A list of page numbers in the update.
+        ordering: A dictionary representing the ordering rules.
+
+    Returns:
+        A list of page numbers in the correct order, or None if a cycle is detected.
+    """
+    relevant_rules = defaultdict(list)
+    in_degree = defaultdict(int)
+    for before, after_list in ordering.items():
+        if before in update:
+            for after in after_list:
+                if after in update:
+                    relevant_rules[before].append(after)
+                    in_degree[after] += 1
+
+    for node in update:
+        if node not in in_degree:
+            in_degree[node] = 0
+
+    queue = [node for node in update if in_degree[node] == 0]
+    sorted_list = []
+
+    while queue:
+        node = queue.pop(0)
+        sorted_list.append(node)
+
+        for neighbor in relevant_rules.get(node, []):
+            in_degree[neighbor] -= 1
+            if in_degree[neighbor] == 0:
+                queue.append(neighbor)
+
+    if len(sorted_list) != len(update):
+        # print('cycle detected')
+        return None
+
+    return sorted_list
+
+
 def part1():
     ordering, updates = get_print_instructions()
-    count = 0
+    total_middle_page = 0
 
     for update in updates:
-        # for each update
-        # check that pages follow the rules
-        pass
+        if is_update_ordered(update, ordering):
+            middle_index = len(update) // 2
+            total_middle_page += update[middle_index]
 
-    print('Part 1:', count)
+    print('Part 1:', total_middle_page)
 
 
 def part2():
-    print('Part 2:')
+    ordering, updates = get_print_instructions()
+    total_middle_page = 0
+
+    for update in updates:
+        if not is_update_ordered(update, ordering):
+            sorted_update = topological_sort(update, ordering)
+            if sorted_update:
+                middle_index = len(sorted_update) // 2
+                total_middle_page += sorted_update[middle_index]
+
+    print('Part 2:', total_middle_page)
 
 
 if __name__ == '__main__':