day 15

aoc2023/day15.py

@@ -0,0 +1,71 @@
+import pathlib
+from collections import defaultdict
+
+base_dir = pathlib.Path(__file__).parent
+filename = base_dir / "day15_input.txt"
+
+with open(base_dir / filename) as f:
+    lines: list[str] = f.read().strip().split(",")
+
+Lens = tuple[str, int]
+
+
+def the_hash_algorithm(input: str) -> int:
+    value = 0
+    for char in input:
+        value += ord(char)
+        value *= 17
+        value %= 256
+    return value
+
+
+def find_lens_index_by_label(lenses: list[Lens], label: str) -> int:
+    for i, lens in enumerate(lenses):
+        if lens[0] == label:
+            return i
+    return -1
+
+
+def part_1():
+    return sum(the_hash_algorithm(line) for line in lines)
+
+
+def part_2():
+    boxes: defaultdict[int, list[Lens]] = defaultdict(list)
+
+    for line in lines:
+        if line.endswith("-"):
+            label = line[:-1]
+            box_number = the_hash_algorithm(label)
+            box_lenses = boxes[box_number]
+
+            lens_index = find_lens_index_by_label(box_lenses, label)
+            if lens_index != -1:
+                box_lenses.pop(lens_index)
+        else:
+            label, focal_length = line.split("=")
+            focal_length = int(focal_length)
+            lens = label, focal_length
+            box_number = the_hash_algorithm(label)
+            box_lenses = boxes[box_number]
+
+            existing_lens_index = find_lens_index_by_label(box_lenses, label)
+
+            if existing_lens_index == -1:
+                box_lenses.append(lens)
+            else:
+                box_lenses[existing_lens_index] = lens
+
+    focal_power = 0
+
+    for box_number, box_lenses in boxes.items():
+        for i, lens in enumerate(box_lenses, start=1):
+            _, focal_length = lens
+            focal_power += (box_number + 1) * focal_length * i
+
+    return focal_power
+
+
+print(f"{the_hash_algorithm('HASH')=}")
+print(f"answer_p1 = {part_1()}")
+print(f"answer_p1 = {part_2()}")

aoc2023/day15_test.txt

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