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.*;

public class Main {
    static Deque<String> list = new ArrayDeque<>();

    public static void main(String[] args) {
        StringBuilder ans = new StringBuilder();
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] sp = new String[2];
        try {
            int n = Integer.parseInt(br.readLine());
            for (int i = 0; i < n; i++) {
                sp = br.readLine().split(" ");
                if (sp[0].equals("insert")) {
                    list.addFirst(sp[1]);
                } else if (sp[0].equals("delete")) {
                    list.remove(sp[1]);
                } else if (sp[0].equals("deleteFirst")) {
                    list.removeFirst();
                } else if (sp[0].equals("deleteLast")) {
                    list.removeLast();
                }
            }
            if (!list.isEmpty()) {
                ans.append(list.getFirst());
                list.removeFirst();
            }
            while (!list.isEmpty()) {
                ans.append(" ").append(list.getFirst());
                list.removeFirst();
            }
            System.out.println(ans.toString());
        } catch (NumberFormatException e) {
            e.printStackTrace();
        }catch (IOException e) {
            e.printStackTrace();
        }
    }
}