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)

use std::io::*;
use std::str::FromStr;
use std::collections::LinkedList;

#[allow(unused_macros)]
macro_rules! scan {
  ($e:expr; $t:ty) => {
    $e.get::<$t>()
  };
  ($e:expr; $($t:ty), *) => {
    ($($e.get::<$t>(),)*)
  }
}

struct Scanner<R: BufRead> {
  reader: R,
  iter: std::vec::IntoIter<String>
}

#[allow(dead_code)]
impl<R: BufRead> Scanner<R> {
  fn new(reader: R) -> Scanner<R> {
    Scanner { reader, iter: vec![String::new()].into_iter() }
  }
  fn new_line(&mut self) {
    let mut line = String::new();
    self.reader.read_line(&mut line).ok();
    self.iter = line.trim().split_whitespace().map(|s| s.to_string()).collect::<Vec<String>>().into_iter();
  }
  fn get<T: FromStr>(&mut self) -> T {
    self.iter.next().unwrap().parse().ok().unwrap()
  }
  fn get_as_vec<T: FromStr>(&mut self) -> Vec<T> {
    self.iter.clone().map(|v| v.parse().ok().unwrap()).collect()
  }
  fn get_line(&mut self) -> String {
    let mut line = String::new();
    self.reader.read_line(&mut line).ok();
    line.trim().to_string()
  }
}

fn main() {
  let cin = stdin();
  let cin = cin.lock();
  let mut sc = Scanner::new(cin);
  sc.new_line();
  let n = scan!(sc; i32);
  let mut list: LinkedList<i32> = LinkedList::new();
  for _ in 0..n {
    sc.new_line();
    let query = scan!(sc; String);
    match &query[..] {
      "insert" => {
        let x = scan!(sc; i32);
        list.push_front(x);
      },
      "delete" => {
        let x = scan!(sc; i32);
        let idx = list.iter().position(|&e| e == x);
        if let Some(idx) = idx {
          let mut s = list.split_off(idx);
          s.pop_front();
          list.append(&mut s);
        }
      },
      "deleteFirst" => {
        list.pop_front();
      },
      "deleteLast" => {
        list.pop_back();
      },
      _ => {}
    } 
  }
  println!("{}", list.iter().map(|e| e.to_string()).collect::<Vec<String>>().join(" "));
}