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;
#[allow(unused_imports)]
use std::collections::*;
#[allow(unused_imports)]
use std::cmp::{min, max};

struct Scanner<R: Read> {
    reader: R,
    buffer: String,
}

#[allow(dead_code)]
impl<R: Read> Scanner<R> {
    fn new(reader: R) -> Scanner<R> {
        Scanner { reader: reader, buffer: String::new() }
    }

    // fn line(&mut self) -> String {
    //     self.buffer = self.reader.by_ref().bytes().map(|c| c.unwrap() as char)
    //         .skip_while(|&c| c == '\n' || c == '\r')
    //         .take_while(|&c| !(c == '\n' || c == '\r'))
    //         .collect::<String>();
    //     self.buffer.clone()
    // }

    fn read_buffer(&mut self) {
        self.buffer = self.reader.by_ref().bytes().map(|c| c.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect::<String>();
    }

    fn safe_read<T: FromStr>(&mut self) -> Option<T> {
        self.read_buffer();
        if self.buffer.is_empty() {
            None
        } else {
            self.buffer.parse::<T>().ok()
        }
    }

    fn read<T: FromStr>(&mut self) -> T {
        if let Some(s) = self.safe_read() {
            s
        } else {
            writeln!(std::io::stderr(), "Terminated with EOF").unwrap();
            std::process::exit(0);
        }
    }

    fn vec<T: FromStr>(&mut self, len: usize) -> Vec<T> {
        (0..len).map(|_| self.read()).collect()
    }

    fn mat<T: FromStr>(&mut self, row: usize, col: usize) -> Vec<Vec<T>> {
        (0..row).map(|_| self.vec(col)).collect()
    }
}

trait Joinable {
    fn join(self, sep: &str) -> String;
}

impl<U: ToString, T: Iterator<Item=U>> Joinable for T {
    fn join(self, sep: &str) -> String {
        self.map(|x| x.to_string()).collect::<Vec<_>>().join(sep)
    }
}

fn main() {
    std::thread::Builder::new()
        .stack_size(104_857_600)
        .spawn(solve)
        .unwrap()
        .join()
        .unwrap();
}

fn solve() {
    let cin = stdin();
    let cin = cin.lock();
    let mut sc = Scanner::new(cin);

    let n: usize = sc.read();
    let mut list: VecDeque<u32> = VecDeque::with_capacity(n + n);

    for _ in 0..n {
        let com: String = sc.read();
        match com.as_str() {
            "insert" => {
                let x = sc.read();
                list.push_front(x);
            },
            "delete" => {
                let x: u32 = sc.read();
                let pos = list.iter().position(|&e| e == x).unwrap_or(list.len());
                let mut tail = list.split_off(pos);
                tail.pop_front();
                list.append(&mut tail);
            },
            "deleteFirst" => {
                list.pop_front();
            },
            "deleteLast" => {
                list.pop_back();
            },
            _ => panic!(),
        }
    }

    println!("{}", list.iter().join(" "));
}