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mjgpy3/aoc-2019-d4p2.hs

Created December 2, 2020 22:11
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aoc-2019-d4p2.hs
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aoc-2019-d4p2.hs
module D4 where
import Control.Monad (guard)
import Data.List (group)
s = 147981
e = 691423
exTwoAdj = elem 2 . map length . group . show
notDecr = go . show
where
go (x:y:rest) = x <= y && go (y:rest)
go [x] = True
go _ = False
possible = do
v <- [s..e]
guard $ exTwoAdj v && notDecr v
pure v
main = print $ length possible
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