Seq.hs

-- For [p_1,p_2 ... p_n]
-- Find three indices i, j and k such that:
-- 1 ≤ i < j < k ≤ n;
-- p_i < p_j and p_j > p_k.
-- Or say that there are no such indices.

func :: S.Seq Int -> String
func sq = let (a,b,c,suc) = S.foldrWithIndex (\ind a (i, j, k, b) ->
                        case b of
                          0 ->
                            case compare a (S.index sq i) of
                              GT -> (ind, 0, 0, b+1)
                              EQ -> (ind, 0, 0, b+1)
                              LT -> (ind, 0, 0, b)

                          1 ->
                            case compare a (S.index sq i) of
                              GT -> (i, ind, k, b+1)
                              EQ -> (i, ind, k, b+1)
                              LT -> (ind, j, k, b)

                          2 ->
                            case compare a (S.index sq j) of
                              GT -> (j, ind, k, b)
                              EQ -> (j, ind, k, b)
                              LT -> (i, j, ind, b+1)

                          3 -> (i, j, k, 3)
                                                        ) (0,0,0,0)  sq

          in case suc of
             3 -> "YES\n" ++ show (c+1) ++ " " ++ show (b+1) ++ " " ++ show (a+1)
             _ -> "NO\n"