Haskell HW 2 Solutions
breakItUp plan:
- replicate input list (length - 3) times
- zip with count
- helper function knows count and list, drop & take
breaklicator xs = replicate (length xs - 3) xs
numberIt ys = zip ys [0..]
breakItUp' :: ([a],Int) -> [a]
breakItUp' (xs,y) = take 4 $ drop y xs
breakItUp_v2 :: [a] -> [[a]]
breakItUp_v2 xs = [ breakItUp' w | w <- numberIt $ breaklicator xs ]
Fancy solution for breakItUp, shows power of Haskell pattern matching (Chapter 4):
breakItUp :: [a] -> [[a]]
breakItUp [a,b,c,d] = [[a,b,c,d]]
breakItUp (x:xs) = (x:take 3 xs) : breakItUp xs
targetPractice plan:
- distance formula
- helper function that remembers the closest point so far
- recursively go through list of all points
-- you should just write (Int,Int) everywhere I write Pt
type Pt = (Int,Int)
dist :: Pt -> Pt -> Int
dist (x0,y0) (x1,y1) = (x1-x0)^2 + (y1-y0)^2
targetPractice :: Pt -> [Pt] -> Pt
targetPractice pt ptList = targetPractice' pt ptList (head ptList)
targetPractice' :: Pt -> [Pt] -> Pt -> Pt
targetPractice' pt [] closestSoFar = closestSoFar
targetPractice' pt (x:xs) closestSoFar = targetPractice' pt xs newClosest
where newClosest = if (dist x pt) < (dist closestSoFar pt)
then x else closestSoFar