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: Accepted)

import java.io.*;
import java.util.Arrays;
import java.util.*;

class Main{
	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine());
		Deque<Integer> stack = new ArrayDeque<Integer>();
		for (int i = 0; i<n ; i++ ) {
			String[] str = (br.readLine()).split(" ");
			if (str[0].equals("deleteFirst")) {
				stack.pollFirst();
			}else if(str[0].equals("deleteLast")){
				stack.pollLast();
			}else{
				int a = Integer.parseInt(str[1]);
				if (str[0].equals("insert")) {
					stack.addFirst(a);
				}else{
					stack.remove(a);
				}
			}
		}
		boolean judge = true;
		int k = 0;
		while(judge){
			try{
				int b = stack.pollFirst();
				if (k == 0) {
					System.out.print(b);
				}else{
					System.out.print(" " + b );
				}
				k++;
			}catch (NullPointerException e){
				judge = false;
				System.out.println("");
			}
		}
	}
}