2021: d06: ex2: add solution

2021/d06/ex2/ex2.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from collections import Counter
+from typing import Iterator, List, TypeVar
+
+T = TypeVar("T")
+
+
+def nth(iterable: Iterator[T], n: int) -> T:
+    return next(itertools.islice(iterable, n, None))
+
+
+def solve(input: List[str]) -> int:
+    fish = [0] * 9
+    for n, count in Counter(map(int, input[0].split(","))).items():
+        fish[n] = count
+
+    def step(fish: List[int]) -> List[int]:
+        # Count how many clones happen
+        new_fish = fish[0]
+
+        # Do the next cycle
+        fish[0:-1] = fish[1:]
+        fish[6] += new_fish
+        fish[8] = new_fish  # Override number of new fish
+
+        return fish
+
+    def iter(fish: List[int]) -> Iterator[List[int]]:
+        while True:
+            yield (fish := step(fish))
+
+    return sum(nth(iter(fish), 256 - 1))
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()