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import Control.Monad
import Data.List
import qualified Data.Map.Strict as Map
modifyAt :: Show a => Int -> (a -> a) -> [a] -> [a]
modifyAt i f l =
let (pre, v : post) = splitAt i l
in pre ++ f v : post
redistribute :: [Int] -> [Int]
redistribute blocks =
let Just idx = findIndex (== maximum blocks) blocks
amt = blocks !! idx
len = length blocks
spread _ 0 b = b
spread i a b = spread (succ i `mod` len) (pred a) (modifyAt i succ b)
in spread (succ idx `mod` len) amt (modifyAt idx (const 0) blocks)
cycledetect :: [Int] -> (Int, Int)
cycledetect blocks = go Map.empty 0 blocks
where
go mp idx bl = case Map.lookup bl mp of
Nothing -> go (Map.insert bl idx mp) (succ idx) (redistribute bl)
Just i -> (idx, idx - i)
main :: IO ()
main = do
blocks <- liftM (map read . words) (readFile "6.in")
let (q1, q2) = cycledetect blocks
print q1
print q2
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