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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.Scanner;

public class Main {
	
	public static void main(String [] args) throws IOException{
		
		ArrayDeque<Integer> list = new ArrayDeque<Integer>();
		BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(reader.readLine());
		String  str;
		StringBuilder builder = new StringBuilder();
		
		for(int i=0; i<n; i++){
			str = reader.readLine();
			if(str.charAt(0) == 'i'){
				list.push(Integer.parseInt(str.substring(7)));
			}else if(str.charAt(6) == ' '){
				list.remove((Integer) Integer.parseInt(str.substring(7)));
			}else if(str.charAt(6) == 'F'){
				list.removeFirst();
			}else{
				list.removeLast();
			}	
		}
		
		builder.append(list.poll());
		for(int num: list){
			builder.append(" ").append(num);
		}
		System.out.println(builder);
	}
  
}