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 JAVA (judge verdict: Time Limit Exceeded)

import java.util.*;

public class Main {
    private static int key[]  = new int[1000002];
    private static int prev[] = new int[1000002];
    private static int next[] = new int[1000002];

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        init();

        int n = sc.nextInt();

        while (n-- > 0) {
            String cmd = sc.next();
            if (cmd.equals("insert"))
                insert(sc.nextInt());
            else if (cmd.equals("delete"))
                delete(sc.nextInt());
            else if (cmd.equals("deleteFirst"))
                deleteFirst();
            else
                deleteLast();
        }
        printKey();
    }
    private static void init() {
        for (int p = 1; p < next.length - 1; p++)
            next[p] = p + 1;
    }
    private static int newCell() {
        int p = next[1];
        next[1] = next[p];
        return p;
    }
    private static void putBack(int p) {
        next[p] = next[1];
        next[1] = p;
    }
    private static void insert(int k) {
        int p = newCell();
        key[p] = k;
        prev[next[0]] = p;
        next[p] = next[0];
        next[0] = p;
        prev[p] = 0;
    }
    private static void delete(int k) {
        for (int p = next[0]; p != 0; p = next[p]) {
            if (key[p] == k) {
                prev[next[p]] = prev[p];
                next[prev[p]] = next[p];
                putBack(p);
                break;
            }
        }
    }
    private static void deleteFirst() {
        int p = next[0];
        prev[next[p]] = prev[p];
        next[prev[p]] = next[p];
        putBack(p);
    }
    private static void deleteLast() {
        int p = prev[0];
        prev[next[p]] = prev[p];
        next[prev[p]] = next[p];
        putBack(p);
    }
    private static void printKey() {
        int first = next[0];
        for (int p = next[0]; p != 0; p = next[p]) {
            if (p != first)
                System.out.print(' ');
            System.out.print(key[p]);
        }
        System.out.println();
    }
}