From ee48bb409a79dfc793316552d9c315990962a67f Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Tue, 21 Dec 2021 15:04:43 +0100
Subject: [PATCH] 2021: d21: ex1: add solution

---
 2021/d21/ex1/ex1.py | 78 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100755 2021/d21/ex1/ex1.py

diff --git a/2021/d21/ex1/ex1.py b/2021/d21/ex1/ex1.py
new file mode 100755
index 0000000..5967837
--- /dev/null
+++ b/2021/d21/ex1/ex1.py
@@ -0,0 +1,78 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from typing import Iterable, Iterator, List, NamedTuple, Tuple, TypeVar
+
+T = TypeVar("T")
+
+
+def grouper(iterable: Iterable[T], n: int) -> Iterator[Tuple[T, ...]]:
+    args = [iter(iterable)] * n
+    return itertools.zip_longest(*args)
+
+
+def take(n: int, iterable: Iterable[T]) -> List[T]:
+    return list(itertools.islice(iterable, n))
+
+
+class PlayerStats(NamedTuple):
+    position: int
+    score: int
+
+
+class GameState(NamedTuple):
+    p1: PlayerStats
+    p2: PlayerStats
+    total_rolls: int
+
+
+WINNING_SCORE = 1000
+
+
+def solve(input: List[str]) -> int:
+    def parse() -> Tuple[int, int]:
+        p1, p2 = input[0].split(" ")[-1], input[1].split(" ")[-1]
+        return int(p1), int(p2)
+
+    def deterministic_die() -> Iterator[int]:
+        return itertools.cycle(range(1, 100 + 1))
+
+    def do_turn(stats: PlayerStats, rolls: Iterator[int]) -> PlayerStats:
+        position, score = stats
+        roll = sum(take(3, rolls))
+        position = ((position - 1 + roll) % 10) + 1
+        score += position
+        return PlayerStats(position, score)
+
+    def play_to_end(intial_state: GameState) -> GameState:
+        p1, p2, total_rolls = intial_state
+        die_rolls = deterministic_die()
+
+        while True:
+            p1 = do_turn(p1, die_rolls)
+            total_rolls += 3
+            if p1.score >= WINNING_SCORE:
+                break
+            p2 = do_turn(p2, die_rolls)
+            total_rolls += 3
+            if p2.score >= WINNING_SCORE:
+                break
+
+        return GameState(p1, p2, total_rolls)
+
+    position1, position2 = parse()
+    p1, p2, total_rolls = play_to_end(
+        GameState(PlayerStats(position1, 0), PlayerStats(position2, 0), 0)
+    )
+    # The loser *must* have the lowest score
+    return min(p1.score, p2.score) * total_rolls
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()