sevenlangs/haskell/DayOne.hs

module DayOne where

-- How many different ways can you find to write allEven?

allEven :: [Integer] -> [Integer]
allEven [] = []
allEven (h:t) = if even h then h:allEven t else allEven t

-- >>> allEven [1, 2, 3, 4, 5, 6]
-- [2,4,6]
--

allEven2 :: [Integer] -> [Integer]
allEven2 xs = [x | x <- xs, even x]

-- >>> allEven2 [1, 2, 3, 4, 5, 6]
-- [2,4,6]
--

allEven3 :: [Integer] -> [Integer]
allEven3 = filter even

-- >>> allEven3 [1, 2, 3, 4, 5, 6]
-- [2,4,6]
--


-- Write a function that takes a list and returns the same list in reverse.

backwards :: [a] -> [a]
backwards = reverse

-- >>> backwards [1, 2, 3, 4]
-- [4,3,2,1]
--

backwards2 :: [a] -> [a]
backwards2 [] = []
backwards2 (x:xs) = backwards2 xs ++ [x]

-- >>> backwards2 [1, 2, 3, 4]
-- [4,3,2,1]
--

-- Write a function that builds two-tuples with all possible combinations of
-- two of the colors black, white, blue, yellow, and red. Note that you should
-- include only one of(black, blue)and(blue, black).

data Color = Black
             | White
             | Blue
             | Yellow
             | Red
             | Green
             deriving (Enum, Ord, Eq, Show)

-- https://stackoverflow.com/questions/4299319/getting-a-list-of-all-possible-data-type-values-in-haskell
allColors :: (Enum a) => [a]
allColors = [toEnum 0 ..]

pairs :: [(Color, Color)]
pairs = [(a, b) | a <- allColors, b <- allColors, a < b]

-- >>> pairs
-- [(Black,White),(Black,Blue),(Black,Yellow),(Black,Red),(White,Blue),(White,Yellow),(White,Red),(Blue,Yellow),(Blue,Red),(Yellow,Red)]
--

-- Write a list comprehension to build a childhood multiplication table. The
-- table would be a list of three-tuples where the first two are integers from
-- 1–12 and the third is the product of the first two.

multiples :: [(Int, Int, Int)]
multiples = [(a, b, a * b) | a <- [0..12], b <- [0..12]]

-- >>> multiples
-- [(0,0,0),(0,1,0),(0,2,0),(0,3,0),(0,4,0),(0,5,0),(0,6,0),(0,7,0),(0,8,0),(0,9,0),(0,10,0),(0,11,0),(0,12,0),(1,0,0),(1,1,1),(1,2,2),(1,3,3),(1,4,4),(1,5,5),(1,6,6),(1,7,7),(1,8,8),(1,9,9),(1,10,10),(1,11,11),(1,12,12),(2,0,0),(2,1,2),(2,2,4),(2,3,6),(2,4,8),(2,5,10),(2,6,12),(2,7,14),(2,8,16),(2,9,18),(2,10,20),(2,11,22),(2,12,24),(3,0,0),(3,1,3),(3,2,6),(3,3,9),(3,4,12),(3,5,15),(3,6,18),(3,7,21),(3,8,24),(3,9,27),(3,10,30),(3,11,33),(3,12,36),(4,0,0),(4,1,4),(4,2,8),(4,3,12),(4,4,16),(4,5,20),(4,6,24),(4,7,28),(4,8,32),(4,9,36),(4,10,40),(4,11,44),(4,12,48),(5,0,0),(5,1,5),(5,2,10),(5,3,15),(5,4,20),(5,5,25),(5,6,30),(5,7,35),(5,8,40),(5,9,45),(5,10,50),(5,11,55),(5,12,60),(6,0,0),(6,1,6),(6,2,12),(6,3,18),(6,4,24),(6,5,30),(6,6,36),(6,7,42),(6,8,48),(6,9,54),(6,10,60),(6,11,66),(6,12,72),(7,0,0),(7,1,7),(7,2,14),(7,3,21),(7,4,28),(7,5,35),(7,6,42),(7,7,49),(7,8,56),(7,9,63),(7,10,70),(7,11,77),(7,12,84),(8,0,0),(8,1,8),(8,2,16),(8,3,24),(8,4,32),(8,5,40),(8,6,48),(8,7,56),(8,8,64),(8,9,72),(8,10,80),(8,11,88),(8,12,96),(9,0,0),(9,1,9),(9,2,18),(9,3,27),(9,4,36),(9,5,45),(9,6,54),(9,7,63),(9,8,72),(9,9,81),(9,10,90),(9,11,99),(9,12,108),(10,0,0),(10,1,10),(10,2,20),(10,3,30),(10,4,40),(10,5,50),(10,6,60),(10,7,70),(10,8,80),(10,9,90),(10,10,100),(10,11,110),(10,12,120),(11,0,0),(11,1,11),(11,2,22),(11,3,33),(11,4,44),(11,5,55),(11,6,66),(11,7,77),(11,8,88),(11,9,99),(11,10,110),(11,11,121),(11,12,132),(12,0,0),(12,1,12),(12,2,24),(12,3,36),(12,4,48),(12,5,60),(12,6,72),(12,7,84),(12,8,96),(12,9,108),(12,10,120),(12,11,132),(12,12,144)]
--

coloring (al, mi, ga, tn, fl) =
  mi /= tn 
  && mi /= al
  && al /= tn
  && al /= mi
  && al /= ga
  && al /= fl
  && ga /= fl
  && ga /= tn

mapcolors = [Red, Green, Blue]

maplayouts = [(al, mi, ga, tn, fl) |
              al <- mapcolors,
              mi <- mapcolors,
              ga <- mapcolors,
              tn <- mapcolors,
              fl <- mapcolors,
              coloring (al, mi, ga, tn, fl)]

-- >>> maplayouts
-- [(Red,Green,Green,Blue,Blue),(Red,Blue,Blue,Green,Green),(Green,Red,Red,Blue,Blue),(Green,Blue,Blue,Red,Red),(Blue,Red,Red,Green,Green),(Blue,Green,Green,Red,Red)]
--