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 <bits/stdc++.h>
using namespace std;
int main()
{
    list <int> ls;
    int n,x;
    string cmd;
    cin>>n;
    for(int i=0;i<n;i++)
    {
       
        cin>>cmd;
        if(cmd=="insert")
        {
            cin>>x;
            ls.push_front(x);
        } 
        else if(cmd=="deleteFirst")
        {
            ls.pop_front();
        }
        else if(cmd=="deleteLast")
        {
            ls.pop_back();
        }
        else if(cmd=="delete")
        {
            cin>>x;
            for(list <int>::iterator it=ls.begin();it!=ls.end();it++)
            {
                if(x==*it)
                {
                    ls.erase(it);
                    break;
                } 
            }
        }
    }

    int i=0;
    for(list <int>::iterator it=ls.begin();it!=ls.end();it++)
    {
        if(i++)
        {
            cout<<" ";
        }
        cout<<*it;
    }
    cout<<endl;
   return 0;
}