Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in Haskell (judge verdict: Memory Limit Exceeded)

import           Control.Applicative
import           Control.Monad
import           Text.Printf

import           Control.Monad.ST
import           Data.STRef

import           Data.Foldable       (toList)
import qualified Data.Sequence       as S

insert :: a -> S.Seq a -> S.Seq a
insert = (S.<|)

delete :: Eq a => a -> S.Seq a -> S.Seq a
delete x s
    | S.null r = s
    | otherwise =
        case S.viewl r of
            x S.:< xs -> l S.>< xs
  where
    (l, r) = S.breakl (== x) s

deleteFirst :: S.Seq a -> S.Seq a
deleteFirst s =
    case S.viewl s of
        x S.:< xs -> xs

deleteLast :: S.Seq a -> S.Seq a
deleteLast s =
    case S.viewr s of
        xs S.:> x -> xs

doCommands :: [[String]] -> [Int]
doCommands css =
    toList $
    runST $ do
        s <- newSTRef (S.empty)
        forM_ css $ \cs -> do
            case cs of
                ["insert", n]   -> modifySTRef' s (insert (read n))
                ["delete", n]   -> modifySTRef' s (delete (read n))
                ["deleteFirst"] -> modifySTRef' s (deleteFirst)
                ["deleteLast"]  -> modifySTRef' s (deleteLast)
        readSTRef s

main :: IO ()
main = do
    return ()
    n <- readLn
    cs <- fmap words <$> replicateM n getLine
    let answer = doCommands cs
    putStrLn $ unwords $ fmap show answer