2024 Day 5 Part 1

2024/src/day05.py

@@ -0,0 +1,53 @@
+import os
+from collections import defaultdict
+from dataclasses import dataclass
+
+
+def relpath(path: str) -> str:
+    return os.path.join(os.path.dirname(__file__), path)
+
+
+with open(relpath("../input/day05.txt")) as f:
+    text = f.read()
+    sections = text.split("\n\n")
+
+    rules = [
+        tuple(map(int, line.split("|")))
+        for line in sections[0].splitlines()
+    ]
+
+    updates = [
+        tuple(map(int, line.split(",")))
+        for line in sections[1].splitlines()
+    ]
+
+
+@dataclass
+class Constraint:
+    before: set[int]
+    after: set[int]
+
+
+def part1(rules, updates):
+    constraints = defaultdict(lambda: Constraint(before=set(), after=set()))
+
+    for (x, y) in rules:
+        constraints[x].after.add(y)
+        constraints[y].before.add(x)
+
+    middles = 0
+    for update in updates:
+        valid = True
+        for (x, y) in zip(update[:-1], update[1:]):
+            if x not in constraints or y in constraints[x].after:
+                continue
+            valid = False
+            break
+
+        if valid:
+            middles += update[int(len(update)) // 2]
+
+    return middles
+
+
+print(part1(rules, updates))