day 5

day_05/part_a.py

@@ -0,0 +1,44 @@
+import aocd
+import collections
+
+def parse_rules(orders):
+    """
+    Return a dictionary mapping page numbers to lists of page numbers
+    For any given key, each page of the value must come after it
+    """
+    rules = collections.defaultdict(list)
+
+    for order in orders:
+        k,v = order.split('|')
+        rules[k].append(v)
+
+    return rules
+
+def verify_update(update, rules):
+    """
+    Ensure that an update is valid using an O(n^2) approach that will
+    bite me in the ass in part B somehow
+    """
+    update = update.split(',')
+    for n, page in enumerate(update):
+        for prev_page in update[:n]:
+            if prev_page in rules[page]:
+                return 0
+    return int(update[len(update)//2])
+
+
+def solve(data):
+    orders, updates = data.split('\n\n')
+    rules = parse_rules(orders.split('\n'))
+    return sum(verify_update(u, rules) for u in updates.split('\n'))
+
+if __name__ == '__main__':
+    puz = aocd.models.Puzzle(year=2024, day=5)
+
+    # data = puz.examples[0].input_data
+    data = puz.input_data
+
+    solution = solve(data)
+
+    print(solution)
+    aocd.submit(solution, year=2024, day=5, part='a')

day_05/part_b.py

@@ -0,0 +1,56 @@
+import aocd
+import collections
+
+def parse_rules(orders):
+    """
+    Return a dictionary mapping page numbers to lists of page numbers
+    For any given key, each page of the value must come after it
+    """
+    rules = collections.defaultdict(list)
+
+    for order in orders:
+        k,v = order.split('|')
+        rules[k].append(v)
+
+    return rules
+
+def update_is_incorrect(update, rules):
+    for n, page in enumerate(update):
+        for prev_n, prev_page in enumerate(update[:n]):
+            if prev_page in rules[page]:
+                return (n, prev_n)
+    return False
+
+
+def fix_update(update, rules):
+    def insert_before(l, a, b):
+        """
+        Mutate l with the bth element moved to just before the ath
+        """
+        l.insert(a, l.pop(b))
+
+    while (indices := update_is_incorrect(update, rules)):
+        insert_before(update, *indices)
+
+    return int(update[len(update)//2])
+
+
+def solve(data):
+    orders, updates = data.split('\n\n')
+    updates = (u.split(',') for u in updates.split('\n'))
+    rules = parse_rules(orders.split('\n'))
+
+    incorrect = (u for u in updates if update_is_incorrect(u, rules))
+    return sum(fix_update(u, rules) for u in incorrect)
+
+if __name__ == '__main__':
+    print('Warning: This is horrifically slow but I do not feel like spending time on a sorting problem', file=__import__('sys').stderr)
+    puz = aocd.models.Puzzle(year=2024, day=5)
+
+    # data = puz.examples[0].input_data
+    data = puz.input_data
+
+    solution = solve(data)
+
+    print(solution)
+    aocd.submit(solution, year=2024, day=5, part='b')