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 C++ (judge verdict: Accepted)

#include <iostream>
#include <list>
#include<cstdio>
using namespace std;

int main() {
    int n, x;
    char com[20];
    list<int> vOut;
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin>>com;
        if(com[0]=='i'){
            cin>>x;
            vOut.push_front(x);
        }else if(com[6]=='F'){
            vOut.pop_front();
        }else if(com[6]=='L'){
            vOut.pop_back();
        }else{
            cin>>x;
            for(list<int>::iterator it=vOut.begin(); it !=vOut.end(); it++){
                if(*it==x){
                    vOut.erase(it);
                    break;
                }
            }
        }
    }
    int i=0;
    for(list<int>:: iterator it=vOut.begin(); it !=vOut.end(); it++){
        if(i++) printf(" ");
        cout<< *it;
    }
    cout<<endl;
}