Day 21

1 files changed, 54 insertions, 0 deletions

diff --git a/day21/part1.hs b/day21/part1.hs
new file mode 100644
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--- /dev/null
+++ b/day21/part1.hs
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+module Part1 (simulate1, makeState1) where
+
+import Debug.Trace (traceShow)
+import Utils
+
+data State = State
+  { positions :: [Int],
+    scores :: [Int],
+    die :: Int,
+    dieRolledTotal :: Int
+  }
+  deriving (Show)
+
+makeState1 = State
+
+rollDie :: State -> (Int, State)
+rollDie prevState = (die prevState, prevState {die = die prevState `mod` 100 + 1})
+
+setAtIndex :: Int -> b -> [b] -> [b]
+setAtIndex i value lst = zip [0 ..] lst $> map (\(i', value') -> if i == i' then value else value')
+
+position player state = positions state !! player
+
+score player state = scores state !! player
+
+move player prevState =
+  let (dieRoll1, state1) = rollDie prevState
+      (dieRoll2, state2) = rollDie state1
+      (dieRoll3, state3) = rollDie state2
+      state = state3 {dieRolledTotal = dieRolledTotal state3 + 3}
+
+      newPos = (position player state + dieRoll1 + dieRoll2 + dieRoll3 - 1) `mod` 10 + 1
+      newScore = score player state + newPos
+   in state
+        { positions = setAtIndex player newPos (positions state),
+          scores = setAtIndex player newScore (scores state)
+        }
+
+checkWinCondition state
+  | (scores state !! 0) >= 1000 = Left (1, scores state !! 1, dieRolledTotal state)
+  | (scores state !! 1) >= 1000 = Left (0, scores state !! 0, dieRolledTotal state)
+  | otherwise = Right state
+
+takeTurn :: Int -> State -> Either (Int, Int, Int) State
+takeTurn player state = do
+  let movedState = move player state
+  checkWinCondition movedState
+
+simulate1 state player =
+  let turnTaken = takeTurn player state
+      nextPlayer = (player + 1) `mod` 2
+   in case turnTaken of
+        Right newState -> simulate1 newState nextPlayer
+        Left result -> result