From bbcc9e1bb30e4775f1344ffb97b15aeecbcd41b2 Mon Sep 17 00:00:00 2001
From: kamoshi <18511281+kamoshi@users.noreply.github.com>
Date: Tue, 22 Dec 2020 15:54:07 +0100
Subject: [PATCH] Update day22.py

---
 2020/Python/day22.py | 58 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/2020/Python/day22.py b/2020/Python/day22.py
index 08443fd..32d47a4 100644
--- a/2020/Python/day22.py
+++ b/2020/Python/day22.py
@@ -39,3 +39,61 @@ def solve_p1(player1: list[int], player2: list[int]) -> int:
 
 PLAYER1, PLAYER2 = parse_data()
 print(solve_p1(PLAYER1, PLAYER2))
+
+
+def play_game(cache: dict[str, int], player1: list[int], player2: list[int]) -> (int, list[int]):
+    previous_rounds: set[str] = set()
+    stack1, stack2 = list(reversed(player1)), list(reversed(player2))
+
+    def round_snapshot() -> str:
+        return f"{stack1}|{stack2}"
+
+    def normal_round() -> None:
+        _number1, _number2 = stack1.pop(), stack2.pop()
+        if _number1 > _number2:
+            stack1.insert(0, _number1)
+            stack1.insert(0, _number2)
+        else:
+            stack2.insert(0, _number2)
+            stack2.insert(0, _number1)
+
+    while len(stack1) > 0 and len(stack2) > 0:
+        if (snapshot := round_snapshot()) in previous_rounds:
+            return 1, stack1
+        else:
+            previous_rounds.add(snapshot)
+
+        if len(stack1) > stack1[len(stack1)-1] and len(stack2) > stack2[len(stack2)-1]:
+            number1, number2 = stack1.pop(), stack2.pop()
+            sub_deck1, sub_deck2 = stack1[1-number1:], stack2[1-number2:]
+
+            # Check cache for winner
+            if (sub_snapshot := f"{sub_deck1}|{sub_deck2}") not in cache:
+                winner, _ = play_game(cache, sub_deck1, sub_deck2)
+                cache[sub_snapshot] = winner
+            else:
+                winner = cache[sub_snapshot]
+
+            if winner == 1:
+                stack1.insert(0, number1)
+                stack1.insert(0, number2)
+            else:
+                stack2.insert(0, number2)
+                stack2.insert(0, number1)
+        else:
+            normal_round()
+
+    if len(stack1) > 0:
+        return 1, stack1
+    else:
+        return 2, stack2
+
+
+# PART 2 is Broken for now
+def solve_p2(player1: list[int], player2: list[int]) -> int:
+    cache: dict[str, int] = {}
+    winner, winning = play_game(cache, player1, player2)
+    return sum(x*y for (x, y) in (zip(winning, [x for x in range(1, len(winning)+1)])))
+
+
+print(solve_p2(PLAYER1, PLAYER2))