2023 day 15.

2023/day15.py

@@ -1,13 +1,31 @@
 import sys
-from collections import defaultdict
+from functools import reduce
-from dataclasses import dataclass
+
+steps = sys.stdin.read().strip().split(",")
+
+
+def _hash(s: str) -> int:
+    return reduce(lambda v, u: ((v + ord(u)) * 17) % 256, s, 0)
 
-lines = sys.stdin.read().splitlines()
 
 # part 1
-answer_1 = ...
+answer_1 = sum(map(_hash, steps))
 print(f"answer 1 is {answer_1}")
 
 # part 2
-answer_2 = ...
+boxes: list[dict[str, int]] = [{} for _ in range(256)]
+
+for step in steps:
+    if (i := step.find("=")) >= 0:
+        label, length = step[:i], int(step[i + 1 :])
+        boxes[_hash(label)][label] = length
+    else:
+        label = step[:-1]
+        boxes[_hash(label)].pop(label, None)
+
+answer_2 = sum(
+    i_box * i_lens * length
+    for i_box, box in enumerate(boxes, start=1)
+    for i_lens, length in enumerate(box.values(), start=1)
+)
 print(f"answer 2 is {answer_2}")

2023/tests/day15.txt

@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7