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 <string>
#include <list>
using namespace std;

int main() {
    int n,i,x;
    string com;
    list<int> L;
    list<int>::iterator it;
    cin>>n;
    for(i=0;i<n;i++){
        cin>>com;
        if(com=="insert"){
            cin>>x;
            L.push_front(x);
        }else if(com=="delete"){
            cin>>x;
            for(it=L.begin();it!=L.end();it++){
                if((*it)==x){L.erase(it);break;}
            }
        }else if(com=="deleteFirst"){
            L.pop_front();
        }else if(com=="deleteLast"){
            L.pop_back();
        }
    }
    if(!L.empty()){
        it=L.begin();
        cout<<(*it);
        for(it++;it!=L.end();it++) cout<<" "<<(*it);
    }
    cout<<endl;
    return 0;
}