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

int main() {
    int n; scanf("%d",&n);
    list<int> v;
    for(int i=0;i<n;i++){
        char com[15]; int x; scanf("%s",com);
        if(com[0]=='i'){
            scanf("%d",&x); v.push_front(x);
        }
        else if(com[6]=='F'){
            v.pop_front();
        }
        else if(com[6]=='L'){
            v.pop_back();
        }
        else if(com[0]=='d'){
            scanf("%d",&x);
            for(list<int>::iterator itr=v.begin();itr!=v.end();++itr){
                if(*itr==x){v.erase(itr); break;}
            }
        }
    }
    int i=0;
    for(list<int>::iterator itr=v.begin();itr!=v.end();++itr){
        if(i++) cout << " ";
        cout << *itr;
    }
    cout << endl;
    return 0;
}