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module Part2 (makeState2, simulate2) where
import Debug.Trace (traceShow)
import Utils
-- (position, score)
type Player = (Int, Int)
type State = (Player, Player)
makeState2 :: Player -> Player -> State
makeState2 p1 p2 = (p1, p2)
win player state = snd (pick player state) >= 21
pick :: Int -> State -> Player
pick 0 = fst
pick 1 = snd
move :: Int -> Int -> (Player, Player) -> State
move delta player state =
let (oldPos, oldScore) = pick player state
newPos = (oldPos + delta - 1) `mod` 10 + 1
newScore = oldScore + newPos
newState = updatePlayer player (newPos, newScore) state
in newState
updatePlayer :: Int -> Player -> State -> State
updatePlayer 0 value (_, other) = (value, other)
updatePlayer 1 value (other, _) = (other, value)
die = [1, 2, 3]
possible3RollSums = [3 .. 9]
coeffs = [1, 3, 6, 7, 6, 3, 1]
simulate2 :: Int -> ((Int, Int), (Int, Int)) -> Integer
simulate2 player state
| win 0 state = 1
| win 1 state = 0
| otherwise =
let (pos, score) = pick player state
nextStates = possible3RollSums $> map (\roll -> move roll player state)
nextStatesWithC = zip coeffs nextStates
nextPlayer = (player + 1) `mod` 2
wins = nextStatesWithC $> map (\(c, nextState) -> c * simulate2 nextPlayer nextState) .> sum
in wins
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