おはよう

べき集合
powerSet :: [Int] -> [[Int]]
powerSet [] = [[]]
powerSet [x] = [[],[x]]
powerSet (x:xs) = (fmap (x:) (powerSet xs))++(powerSet xs)

べき集合の中から長さがnのものだけ抜き出す
comb :: Int -> [Int] -> [[Int]]
comb n k = filter ((n ==) . length) (powerSet k)