2023 day 15

Author: sanderploegsma

2023/python/aoc_2023/day15.py

@@ -0,0 +1,63 @@
+"""Advent of Code 2023, Day 15: Lens Library."""
+
+import sys
+from typing import TextIO
+
+
+def hash(step: str):
+    value = 0
+    for c in step:
+        value += ord(c)
+        value *= 17
+        value %= 256
+    return value
+
+
+def index_of(items, predicate):
+    return next((idx for idx, item in enumerate(items) if predicate(item)), -1)
+
+
+def part_one(file: TextIO) -> int:
+    """Solve part one of the puzzle."""
+    steps = file.read().strip().split(",")
+    return sum(map(hash, steps))
+
+
+def part_two(file: TextIO) -> int:
+    """Solve part two of the puzzle."""
+    steps = file.read().strip().split(",")
+    boxes = {i: [] for i in range(256)}
+    for step in steps:
+        if "-" in step:
+            label = step[:-1]
+            i = hash(label)
+            if (idx := index_of(boxes[i], lambda item: label in item)) >= 0:
+                boxes[i].pop(idx)
+        if "=" in step:
+            label = step[:-2]
+            i = hash(label)
+            if (idx := index_of(boxes[i], lambda item: label in item)) >= 0:
+                boxes[i].pop(idx)
+                boxes[i].insert(idx, step)
+            else:
+                boxes[i].append(step)
+
+    def box_value(box: int) -> int:
+        return (box + 1) * sum((i + 1) * int(item[-1]) for i, item in enumerate(boxes[box]))
+
+    return sum(map(box_value, boxes.keys()))
+
+
+def main():
+    """The main entrypoint for the script."""
+    filename = sys.argv[0].replace(".py", ".txt")
+
+    with open(filename, encoding="utf-8") as file:
+        print("Part one:", part_one(file))
+
+    with open(filename, encoding="utf-8") as file:
+        print("Part two:", part_two(file))
+
+
+if __name__ == "__main__":
+    main()