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 C# (judge verdict: Wrong Answer)

using System;

namespace ALDS1_3_C
{
    class Program
    {
        static void Main(string[] args)
        {
            DoublyLinkedList List = new DoublyLinkedList();
            string str1 = Console.ReadLine();
            int n = int.Parse(str1);
            for (int i = 0; i < n; ++i)
            {
                string[] str = Console.ReadLine().Split(' ');
                if (str[0] == "insert")
                {
                    int x = int.Parse(str[1]);
                    List.insert(x);
                }
                else if (str[0] == "delete")
                {
                    int x = int.Parse(str[1]);
                    List.delete(x);
                }
                else if (str[0] == "deleteFirst")
                {
                    List.deleteFirst();
                }
                else if (str[0] == "deleteLast")
                {
                    List.deleteLast();
                }
            }
            List.output();
//            Console.ReadLine();
        }

        struct DoublyLinkedListElement
        {
            public int prev;
            public int next;
            public int key;
        }

        class DoublyLinkedList
        {
            int MAX = 1000020;
            DoublyLinkedListElement[] element;
            int last;
            int first;

            public DoublyLinkedList()
            {
                element = new DoublyLinkedListElement[MAX];
                initialize();
            }

            private void initialize()
            {
                last = 0;
                first = 1;
                element[last].prev = first;
                element[last].next = last;
                element[first].next = last;
                element[first].prev = first;
            }

            public void insert(int x)
            {
                int cursor = first;
                first = (first + 1) % MAX;
                element[cursor].key = x;
                element[cursor].prev = first;
                element[first].prev = first;
                element[first].next = cursor;
            }

            public void delete(int x)
            {
                int cursor = element[first].next;
                for (int i = 0; i < 20; ++i) 
                {
                    if (element[cursor].key == x)
                    {
                        element[element[cursor].prev].next = element[cursor].next;
                        element[element[cursor].next].prev = element[cursor].prev;
                        break;
                    }
                    cursor = element[cursor].next;
                }
            }

            public void deleteFirst()
            {
                first = element[first].next;
                element[first].prev = first;
            }

            public void deleteLast()
            {
                last = element[last].prev;
                element[last].next = last;
            }

            public void output()
            {
                if (element[first].next == last)
                {
                    Console.WriteLine("");
                }
                else
                {
                    int cursor = element[first].next;
                    Console.Write("{0}", element[cursor].key);
                    while (true)
                    {
                        cursor = element[cursor].next;
                        if (cursor == element[cursor].next)
                        {
                            Console.Write("\n");
                            break;
                        }
                        Console.Write(" {0}", element[cursor].key);
                    }
                }
            }
        }
    }
}