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.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        DoublyLinkedList list = new DoublyLinkedList();
        for (int i = 0; i < n; i++) {
            String c = scanner.next();
            if ("insert".equals(c)) {
                list.insert(scanner.nextInt());
            } else if ("delete".equals(c)) {
                list.delete(scanner.nextInt());
            } else if ("deleteFirst".equals(c)) {
                list.deleteFirst();
            } else {
                list.deleteLast();
            }
        }
        list.print();
    }

    private static class DoublyLinkedList {
        private static class Node {
            int i;
            Node next;
            Node prev;

            private Node(int i) {
                this.i = i;
            }
        }

        Node first;
        Node last;

        private void insert(int i) {
            Node node = new Node(i);
            if (first != null) {
                first.prev = node;
                node.next = first;
            }
            first = node;
            if (last == null) {
                last = node;
            }
        }

        private void delete(int i) {
            Node node = first;
            while (node != null) {
                if (node.i == i) {
                    if (node.prev != null && node.next != null) {
                        node.prev.next = node.next;
                        node.next.prev = node.prev;
                    } else if (node.prev != null) {
                        deleteLast();
                    } else if (node.next != null) {
                        deleteFirst();
                    } else {
                        first = last = null;
                    }
                    break;
                }
                node = node.next;
            }
        }

        private void deleteFirst() {
            if (first.next != null) {
                first.next.prev = null;
                first = first.next;
            } else {
                first = last = null;
            }
        }

        private void deleteLast() {
            if (last.prev != null) {
                last.prev.next = null;
                last = last.prev;
            } else {
                first = last = null;
            }
        }

        private void print() {
            Node node = first;
            StringBuilder sb = new StringBuilder();
            while (node != null) {
                sb.append(node.i);
                if (node.next != null) {
                    sb.append(" ");
                }
                node = node.next;
            }
            System.out.println(sb.toString());
        }
    }
}