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 Rust (judge verdict: Accepted)

fn main() {
    let stdin = std::io::stdin();
    let mut buf = String::new();
    stdin.read_line(&mut buf).ok();
    let n: usize = buf.trim().parse().unwrap_or(0);

    let mut dll = Vec::new();

    let mut head = 0;

    for _ in 0..n {
        //println!("{:?}",dll);
        let mut buf = String::new();
        stdin.read_line(&mut buf).ok();
        let vec: Vec<&str> = buf.split_whitespace().collect();

        if vec[0] == "insert" {
            dll.push(vec[1].parse().unwrap_or(0));
        } else if vec[0] == "delete" {
            for j in (head..dll.len()).rev() { 
                if vec[1].parse().unwrap_or(0) == dll[j] { 
                    dll.remove(j); 
                    break; 
                } 
            }
        } else if vec[0] == "deleteFirst" {
            dll.pop();
        } else if vec[0] == "deleteLast" {
            head += 1;
        }
    }
    for i in (head..dll.len()).rev() {
        print!("{}", dll[i]);
        if i == head {
            break;
        }
        print!(" ");
    }
    println!();
}