homework1.hs

{-# OPTIONS_GHC -Wall #-}

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-- Exercise 1
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toDigits    :: Integer -> [Integer]
toDigitsRev :: Integer -> [Integer]

toDigitsRev n
  | n < 1     = []
  | n < 10    = [n]
  | otherwise = (n `mod` 10) : (toDigitsRev (n `div` 10))

toDigits = reverse . toDigitsRev

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-- Exercise 2
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doubleEveryOther :: [Integer] -> [Integer]
doubleEveryOther' :: [Integer] -> [Integer]

doubleEveryOther' [] = []
doubleEveryOther' (x:[]) = [x]
doubleEveryOther' (x:(y:zs)) = x : (2*y) : doubleEveryOther'(zs)

doubleEveryOther = reverse . doubleEveryOther' . reverse

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-- Exercise 3
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sumDigits :: [Integer] -> Integer
sumDigits xs = foldl (+) 0 (map (\x -> foldl (+) 0 (toDigits x)) xs)

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-- Exercise 4
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validate :: Integer -> Bool
validate n = ((sumDigits (doubleEveryOther (toDigits n))) `rem` 10) == 0

-- main = putStrLn (show (validate 4012888888881881))

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-- Exercise 5
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type Peg = String
type Move = (Peg, Peg)

hanoi :: Integer -> Peg -> Peg -> Peg -> [Move]

hanoi 1 a b _ = [(a,b)]
hanoi n a b c = concat [(hanoi (n-1) a c b), [(a,b)], (hanoi (n-1) c b a)]