fib :: Int -> Int
fib n
    | n <= 1 = n
    | otherwise = fib (n-1) + fib (n-2)

above :: Int -> [Int] -> Bool
above x [] = True
above x (y : ys) = x >= y && above x ys

pari :: Int -> [(Int, Int)]
pari n = [(i, j) | i <- [1..n], j <- [i+1..n]]


-- problem n dam
type Square = (Int, Int)
type Queen = Square

board :: Int -> [Square]
board n = [(i,j) | i <- [1..n], j <- [1..n]]

attacks :: Queen -> Square -> Bool
attacks (a,b) (u,v) = (a == u) || (b == v) || (abs (a - u) == abs (b - v))

attack :: [Queen] -> Square -> Bool
attack [] _ = False
attack (q : qs) x = attacks q x || attack qs x

available :: [Queen] -> [Square] -> [Square]
available qs xs = [x | x <- xs, not (attack qs x)]

place1 :: Int -> Int -> [Queen] -> [Queen]
place1 n x qs = [(x,y) | y <- [1..n], not (attack qs (x,y))] 

queens :: Int -> [[Queen]]
queens n = place 1 []
  where
    place x qs
      | x > n = [qs]
      | otherwise = concat [place (x+1) (q:qs) | q <- place1 n x qs]

-- drobiz
drobiz :: [Int] -> Int -> [[Int]]
drobiz xs y = search [] y
    where search ys y
        | y == 0 = [ys]
        | y < 0 = []
        | otherwise = concat [search (x:ys) (y-x) | x <- xs, above x ys]