Implement day 5 solver

puzzles/5.py

@@ -0,0 +1,112 @@
+from typing import Iterator
+
+
+test_input_p1 = """
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47
+""".strip()
+test_input_p2 = test_input_p1
+
+test_solution_p1 = 143
+test_solution_p2 = 123
+
+
+def solve_p1(puzzle_input: str) -> int:
+    rules, updates = _parse_rules_and_updates(puzzle_input)
+    return sum(
+        update[len(update) // 2]
+        for update in updates
+        if _is_correctly_ordered(rules, update)
+    )
+
+
+def solve_p2(puzzle_input: str) -> int:
+    rules, updates = _parse_rules_and_updates(puzzle_input)
+    corrected_updates = (
+        _fix_update(rules, update)
+        for update in updates
+        if not _is_correctly_ordered(rules, update)
+    )
+    return sum(update[len(update) // 2] for update in corrected_updates)
+
+
+OrderingRules = dict[int, set[int]]
+Update = tuple[int, ...]
+
+
+def _parse_rules_and_updates(
+    puzzle_input: str,
+) -> tuple[OrderingRules, Iterator[Update]]:
+    ordering_rules, _, updates = puzzle_input.partition("\n\n")
+
+    rules: OrderingRules = {}
+    for line in ordering_rules.strip().split("\n"):
+        a, _, b = line.partition("|")
+        a, b = int(a), int(b)
+        if b not in rules:
+            rules[b] = set()
+        rules[b].add(a)
+
+    return (
+        rules,
+        (tuple(map(int, line.split(","))) for line in updates.strip().split("\n")),
+    )
+
+
+def _is_correctly_ordered(rules: OrderingRules, update: Update) -> bool:
+    contains = set(update)
+    seen = set()
+
+    for i in update:
+        for j in rules.get(i, ()):
+            if j in contains and j not in seen:
+                return False
+        seen.add(i)
+
+    return True
+
+
+def _fix_update(rules: OrderingRules, update: Update) -> Update:
+    contains = set(update)
+    seen = set()
+
+    fixed_update = list()
+
+    def _fix_item(i):
+        for j in rules.get(i, ()):
+            if j in contains and j not in seen:
+                _fix_item(j)
+        fixed_update.append(i)
+        seen.add(i)
+
+    for i in update:
+        if i not in seen:
+            _fix_item(i)
+
+    return tuple(fixed_update)