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.util.*;
import java.lang.*;
import java.io.*;

class Main {
	public static void main (String[] args) throws java.lang.Exception {
		// your code goes here
		BufferedReader stdReader = new BufferedReader(new InputStreamReader(System.in));
		String line = stdReader.readLine();
		int n = Integer.valueOf(line);
		LinkedList<Integer> li = new LinkedList<Integer>();
		for(int i = 0; i < n; i++) {
			line = stdReader.readLine();
			String[] sss = line.split(" ");
			if(sss[0].equals("insert")) {
				Integer o = Integer.valueOf(sss[1]);
				li.add(0, o);
			}else if(sss[0].equals("delete")){
				Integer o = Integer.valueOf(sss[1]);
				li.remove((Object) o);
			}else if(sss[0].equals("deleteFirst")) {
				li.remove(0);
			}else if(sss[0].equals("deleteLast")) {
				li.remove(li.size()-1);
			}
		}
		result(li);
	}
	public static void print(String s) {
		System.out.println(s);
	}
	public static void result(LinkedList<Integer> li) {
		StringBuilder bu = new StringBuilder();
		for(Integer i: li) {
			if(bu.length() > 0) {
				bu.append(" ");
			}
			bu.append(i);
		}
		print(bu.toString());
	}
}