Add Drew's day 22 solution

Drew/drew_day22.py

@@ -0,0 +1,118 @@
+from typing import Deque, List, Set, Tuple
+from collections import deque
+
+
+TEST_INPUT = """Player 1:
+9
+2
+6
+3
+1
+
+Player 2:
+5
+8
+4
+7
+10""".split(
+    "\n\n"
+)
+
+with open("day22.txt") as infile:
+    REAL_INPUT = infile.read().split("\n\n")
+
+
+def build_hands(puzzle_input: List[str]) -> List[Deque[int]]:
+    result = []
+    for hand_desc in puzzle_input:
+        result.append(
+            deque(
+                list(
+                    int(i) for hand in hand_desc.splitlines()[1:] for i in hand.split()
+                )
+            )
+        )
+    return result
+
+
+class GameOver(Exception):
+    pass
+
+
+def play_round(hands: List[Deque[int]], part_two: bool = False):
+    try:
+        p1_card = hands[0].popleft()
+    except IndexError as exc:
+        raise GameOver() from exc
+    try:
+        p2_card = hands[1].popleft()
+    except IndexError as exc:
+        # put the player 1 card back in the deck
+        hands[0].appendleft(p1_card)
+        raise GameOver() from exc
+    if part_two:
+        if len(hands[0]) >= p1_card and len(hands[1]) >= p2_card:
+            new_hands = [
+                deque(list(hands[0])[:p1_card]),
+                deque(list(hands[1])[:p2_card]),
+            ]
+            winner_score = play_game(new_hands, True)
+            if winner_score == score_hand(new_hands[0]):
+                hands[0].append(p1_card)
+                hands[0].append(p2_card)
+            elif winner_score == score_hand(new_hands[1]):
+                hands[1].append(p2_card)
+                hands[1].append(p1_card)
+            else:
+                raise ValueError("unknown winner score")
+            return
+    if p1_card > p2_card:
+        hands[0].append(p1_card)
+        hands[0].append(p2_card)
+    elif p2_card > p1_card:
+        hands[1].append(p2_card)
+        hands[1].append(p1_card)
+    else:
+        raise ValueError("same card should not be possible")
+
+
+def score_hand(hand: Deque[int]) -> int:
+    hand_length = len(hand)
+    return sum(value * (hand_length - index) for index, value in enumerate(hand))
+
+
+def part_one(puzzle_input: List[str], part_two: bool = False) -> int:
+    hands = build_hands(puzzle_input)
+    return play_game(hands, part_two)
+
+
+def play_game(hands: List[Deque[int]], part_two: bool = False) -> int:
+    turns = 0
+    hands_seen: Set[Tuple[Tuple[int]]] = set()
+    while True:
+        if part_two:
+            active_hands = tuple(tuple(i) for i in hands)
+            if active_hands in hands_seen:
+                return score_hand(hands[0])
+            hands_seen.add(active_hands)
+        try:
+            play_round(hands, part_two=part_two)
+        except GameOver:
+            scores = [score_hand(hand) for hand in hands]
+            assert (scores[0] == 0) is not (scores[1] == 0)
+            return [i for i in scores if i != 0][0]
+        else:
+            turns += 1
+
+
+def main():
+    p1_score = part_one(TEST_INPUT)
+    assert p1_score == 306, p1_score
+    print(part_one(REAL_INPUT))
+    p2_score = part_one(TEST_INPUT, True)
+    assert p2_score == 291, p2_score
+    print(part_one(REAL_INPUT, True))
+
+
+if __name__ == "__main__":
+    main()