2017: d10: ex1: add solution

2017/d10/ex1/ex1.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+
+import copy
+import sys
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[int]:
+        return [int(n) for n in input.split(",")]
+
+    def run_round(lengths: list[int], circle: list[int]) -> list[int]:
+        circle = copy.deepcopy(circle)
+        cur_pos = 0
+        skip_size = 0
+        for n in lengths:
+            # Invalid length
+            if n > len(circle):
+                continue
+            # Reverse
+            for i, j in zip(
+                range(cur_pos, cur_pos + n // 2),
+                # Avoid off-by-one by going further than necessary
+                range(cur_pos + n - 1, cur_pos, -1),
+            ):
+                i %= len(circle)
+                j %= len(circle)
+                circle[i], circle[j] = circle[j], circle[i]
+            # Move
+            cur_pos += n + skip_size
+            # Increase
+            skip_size += 1
+        return circle
+
+    lengths = parse(input)
+    circle = list(range(256))
+    circle = run_round(lengths, circle)
+    return circle[0] * circle[1]
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()