Problem

Time limit : 2sec / Memory limit : 256MB

Problem Statement
The season for Snuke Festival has come again this year. First of all, Ringo will perform a ritual to summon Snuke. For the ritual, he needs an altar, which consists of three parts, one in each of the three categories: upper, middle and lower.
He has N parts for each of the three categories. The size of the i-th upper part is Ai, the size of the i-th middle part is Bi, and the size of the i-th lower part is Ci.
To build an altar, the size of the middle part must be strictly greater than that of the upper part, and the size of the lower part must be strictly greater than that of the middle part. On the other hand, any three parts that satisfy these conditions can be combined to form an altar.
How many different altars can Ringo build? Here, two altars are considered different when at least one of the three parts used is different.

Constraints
1≤N≤10^5
1≤Ai≤10^9(1≤i≤N)
1≤Bi≤10^9(1≤i≤N)
1≤Ci≤10^9(1≤i≤N)
All input values are integers.

Input
Input is given from Standard Input in the following format:
N
A1 … AN
B1 … BN
C1 … CN

Output
Print the number of different altars that Ringo can build.

Sample Input1

2 1 5 2 4 3 6 

Sample Output1

3 

Sample Input2

3 1 1 1 2 2 2 3 3 3 

Sample Output2

27 

Sample Input3

6 3 14 159 2 6 53 58 9 79 323 84 6 2643 383 2 79 50 288 

Sample Output3

87 

My solution as Time Limit Exceeded:

import qualified Data.Char as Char import qualified Data.List as List import qualified Data.Maybe as Maybe import qualified Text.Printf as Printf import qualified Control.Monad as Monad import qualified Data.Array as Array  bisectLeft :: (Ord a) => a -> (Array.Array Int a) -> Int bisectLeft n xs = bisectLeft' 0 (length xs) n xs  bisectLeft' :: (Ord a) => Int -> Int -> a -> (Array.Array Int a) -> Int bisectLeft' lo hi n xs = if lo >= hi then lo else                     if n <= (xs Array.! mid) then bisectLeft' lo mid n xs                       else bisectLeft' (mid + 1) hi n xs                     where mid = (lo + hi) `div` 2  bisectRight :: (Ord a) => a -> (Array.Array Int a) -> Int bisectRight n xs = bisectRight' 0 (length xs) n xs  bisectRight' :: (Ord a) => Int -> Int -> a -> (Array.Array Int a) -> Int bisectRight' lo hi n xs = if lo >= hi then hi else                     if n < (xs Array.! mid) then bisectRight' lo mid n xs                       else bisectRight' (mid + 1) hi n xs                     where mid = (lo + hi) `div` 2  main :: IO () main = do   n <- (read :: String -> Int) <$  > getLine   as <- (Array.listArray (0,n-1)) . List.sort . map (read :: String -> Int) . words <$  > getLine   bs <- map (read :: String -> Int) . words <$  > getLine   cs <- (Array.listArray (0,n-1)) . List.sort . map (read :: String -> Int) . words <$  > getLine   print $   foldl (+) 0 $   map (\ b -> (bisectLeft b as) * (n - bisectRight b cs)) bs 

I think it takes too much time to make array, but I cannot think of any way to make it more efficient…
How can I this code more efficient?

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