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  1. Prepare
  2. Functional Programming
  3. Recursion
  4. Concave Polygon
  5. Discussions

Concave Polygon

  • [deleted]     + 1 comment

    cool, got to re-use code for the convex hull problem: 

    insert :: [Point] -> Point -> [Point]
insert vs v = case vs of
  (x:y:z:ws) -> case orientation v x y of
    Up -> insert (tail vs) v
    _ -> v : vs
  _ -> v : vs

convexHull :: [Point] -> [Point]
convexHull = foldl' insert []

convex :: [Point] -> Bool
convex xs = length xs == length (convexHull xs)

concave = not . convex

solve :: [Point] -> String
solve xs
  | concave xs = "YES"
  | otherwise  = "NO"