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: Runtime Error)

// Doubly_Linked_List.cs

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Diagnostics;

class Doubly_Linked_List {
	public static void Main(string[] args) {


		int n = int.Parse(Console.ReadLine());

		var<string> list = new LinkedList<string>();

		for(int i = 0; i < n; i++) {
			list.AddLast(Console.ReadLine());
		}

		string[] str = new string[n];
		int count = 0;
		int num_c = 1;
		foreach(string s in list) {

			if(s.IndexOf("insert") >= 0) {
				var r = new Regex(@"[^0-9]");
				str[count] = r.Replace(s, "");
				num_c++;
			}

			if(s.IndexOf("deleteFirst") >= 0) {
				List<string> numlist = new List<string>(str);
				numlist.RemoveAt(0);
				str = numlist.ToArray();
				num_c--;
			}

			if(s.IndexOf("deleteLast") >= 0) {
				List<string> numlist = new List<string>(str);
				numlist.RemoveAt(num_c);
				str = numlist.ToArray();
				num_c--;
			}
 
			if(s.IndexOf("delete ") >= 0) {
				var r = new Regex(@"[^0-9]");

				for(int i = 0; i < str.Length; i++) {
					if(str[i] == r.Replace(s, "")) {
						List<string> numlist = new List<string>(str);
						numlist.RemoveAt(i);
						str = numlist.ToArray();
					}
				}
				num_c--;
			}
			count++;
		}

		Array.Reverse(str);
		string moji = "";
		for(int i = 0; i < str.Length; i++) {
			moji += str[i];
		}

		var reg = new Regex(@"[^0-9]");
		moji = reg.Replace(moji, "");

		int len = moji.Length;

		for(int i = 0; i < len; i++) {
			Console.Write(moji[i]);
			if(i != len - 1) {
				Console.Write(" ");
			} else {
				Console.WriteLine();
			}
		}

	}

}