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++11 (judge verdict: Accepted)

//#include<iostream>//list<> l,size() push_front(x) push_back(x) pop_front() pop_back() front() back() begin() end() insert(p,x) erase(p) clear()
#include<cstdio>//vector<> v, v.size(), v.push_back(), v.pop_back(), v.begin(), v.end(), v.insert(p,x), v.erase(p), v.clear();p:µü´úÆ÷
#include<list>//both vector and list can use "[]" list insert and delete only need O(1), vector O(n).
//#include<algorithm>
using namespace std;
int main()
{

  int q, x;
  char com[20];
  list<int> v;
  scanf("%d", &q);
  for(int i=0; i<q; i++)
  {
    scanf("%s", com);
    if(com[0] == 'i')
    {
      scanf("%d", &x);
      v.push_front(x);
    }
    else if(com[6] == 'L')
      v.pop_back();
    else if(com[6] == 'F')
      v.pop_front();
    else if(com[0] == 'd')
    {
      scanf("%d", &x);
      for(list<int>::iterator it = v.begin(); it != v.end(); it++)
      {
        if(*it == x)
        {
          v.erase(it);
          break;
        }
      }
    }
  }
  int i=0;
  for(list<int>::iterator it = v.begin(); it!=v.end(); it++)
  {
    if(i++)
      printf(" ");
    printf("%d", *it);
  }
  printf("\n");
  return 0;
}