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module Main where
import Data.Char
import Numeric
pairs :: String -> [(Char,Char)]
pairs (a:b:cs) = (a,b) : pairs (b:cs)
pairs _ = []
allEqual :: (Eq a) => [a] -> Bool
allEqual (a:b:cs) = if a /= b then False else allEqual (b:cs)
allEqual _ = True
hasStraight :: String -> Bool
hasStraight (a:b:c:ds) = (y == x + 1 && z == x + 2) || hasStraight (b:c:ds)
where (x,y,z) = (ord a,ord b,ord c)
hasStraight _ = False
hasForbidden :: String -> Bool
hasForbidden [] = False
hasForbidden (x:xs) = x /= 'i' && x /= 'o' && x /= 'l' && not (hasForbidden xs)
hasTwoPairs :: String -> Bool
hasTwoPairs s = (not.allEqual) $ filter (\(a,b) -> a == b) (pairs s)
isValid :: String -> Bool
isValid s = hasStraight s && not (hasForbidden s) && hasTwoPairs s
show26 :: Int -> String
show26 n = showIntAtBase 26 (\d -> chr (97 + d)) n ""
read26 :: String -> Int
read26 = fst . head . readInt 26 (\c -> let o = ord c in 97 <= o && o <= 122) (\c -> ord c - 97)
pad :: Int -> Char -> String -> String
pad n c s = if length s < n then pad n c (c:s) else s
nextpass :: String -> String
nextpass s = pad (length s) 'a' $ show26 $ succ $ read26 s
nextvalidpass :: String -> String
nextvalidpass = head . dropWhile (not . isValid) . iterate nextpass
day11 :: IO ()
day11 = do
print $ nextvalidpass $ nextpass $ nextvalidpass "cqjxjnds"
main = day11
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