diff options
| -rw-r--r-- | lec01/hw.hs | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/lec01/hw.hs b/lec01/hw.hs index 491d74d..8f4197d 100644 --- a/lec01/hw.hs +++ b/lec01/hw.hs @@ -1 +1,42 @@ -- homework for lecture 1 + +-- exercise 1 + +toDigits :: Integer -> [Integer] +toDigits n + | n > 0 = toDigits (n `div` 10) ++ [n `mod` 10] + | otherwise = [] + +revList :: [Integer] -> [Integer] +revList [] = [] +revList (x:xs) = revList xs ++ [x] + +toDigitsRev :: Integer -> [Integer] +toDigitsRev n = revList (toDigits n) + +-- exercise 2 + +-- [SIDE NOTE] The exercise specifies that the function below "should double +-- every other number *beginning from the right*". However, it's unclear +-- whether this is a requirement (i.e. the function must double digits in +-- reverse order) or a mere clarification to better understand which numbers +-- should be doubled and which not. Since the order doesn't matter (and doing +-- the operation in reverse order would also complicate the solution), I +-- decided to do it from left to right, the usual order. +doubleEveryOther :: [Integer] -> [Integer] +doubleEveryOther [] = [] +doubleEveryOther (x:y:ys) = x*2 : (y : doubleEveryOther ys) + +-- exercise 3 + +-- This function assumes that the list only contains numbers between 0 and 19 +sumDigits :: [Integer] -> Integer +sumDigits [] = 0 +sumDigits (x:xs) + | x >= 10 = (1 + x `mod` 10) + sumDigits xs + | otherwise = x + sumDigits xs + +-- exercise 4 + +validate :: Integer -> Bool +validate n = sumDigits (doubleEveryOther (toDigits n)) `mod` 10 == 0 |