2023: d15: ex2: add solution

2023/d15/ex2/ex2.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python
+
+import dataclasses
+import sys
+from typing import Optional
+
+
+@dataclasses.dataclass
+class Lens:
+    label: str
+    num: int
+
+    def __eq__(self, other: object) -> bool:
+        if isinstance(other, str):
+            return self.label == other
+        return super().__eq__(other)
+
+
+def solve(input: list[str]) -> int:
+    def compute_hash(string: str) -> int:
+        res = 0
+
+        for c in string:
+            res += ord(c)
+            res *= 17
+            res %= 256
+
+        return res
+
+    def parse_step(step: str) -> tuple[str, Optional[int]]:
+        if step[-1] == "-":
+            return step[:-1], None
+        label, num = step.split("=")
+        return label, int(num)
+
+    def find_label(label: str, box: list[Lens]) -> Optional[int]:
+        for i, lens in enumerate(box):
+            if lens.label == label:
+                return i
+        return None
+
+    def focusing_power(boxes: list[list[Lens]]) -> int:
+        res = 0
+
+        for box_num, box in enumerate(boxes, start=1):
+            for i, lens in enumerate(box, start=1):
+                res += box_num * i * lens.num
+
+        return res
+
+    boxes: list[list[Lens]] = [[] for _ in range(256)]
+
+    for label, num in map(parse_step, input):
+        box = compute_hash(label)
+        index = find_label(label, boxes[box])
+        if num is None:
+            # Remove label from box
+            if index is not None:
+                del boxes[box][index]
+        # Place len in box
+        elif index is not None:
+            boxes[box][index].num = num
+        else:
+            boxes[box].append(Lens(label, num))
+
+    return focusing_power(boxes)
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    assert len(input) == 1  # Sanity check
+    print(solve(input[0].split(",")))
+
+
+if __name__ == "__main__":
+    main()