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: Time Limit Exceeded)

#include"stdio.h"
#include"stdlib.h"
#include"string.h"

struct Vector
{
  int x;
  struct Vector *next;
};
struct Vector *head;
struct Vector *end;
void setVector()
{
  head=(struct Vector*)malloc(sizeof(struct Vector));
  head->next = NULL;
  end = head;
}
void push_back(int key)
{
  struct Vector *new;
  new = (struct Vector*)malloc(sizeof(struct Vector));
  new->next = head->next;
  head->next=new;
  new->x = key;
}
void Delete(int key)
{
  struct Vector *buf;
  struct Vector *p;
  for(p=head;p->next!=NULL;p=p->next)
    {
      if(p->next->x==key)
        {
          if(p->next->next==NULL)
            {
              buf=p->next;
              p->next=NULL;
              free(buf);
              break;
            }
          else
            {
              buf=p->next;
              p->next=p->next->next;
              free(buf);
              break;
            }
        }
    }
}
void Delete_flont()
{
  struct Vector *buf;
  if(head->next!=NULL)
    {
      buf=head->next;
      head->next=head->next->next;
      free(buf);
    }
}
void Delete_back()
{
  struct Vector *buf;
  struct Vector *p;
  if(head->next!=NULL)
    {
      for(p=head;p->next->next!=NULL;p=p->next);
      buf=p->next;
      p->next=p->next->next;
      free(buf);
    }
}
int main()
{
  setVector();
  int i;
  struct Vector* p;
  int n;
  int key;
  char cmd[12];
  char insert[]={"insert"};
  char delete[]={"delete"};
  char deleteFirst[]={"deleteFirst"};
  char deleteLast[]={"deleteLast"};
  scanf("%d",&n);
  for(i=0;i<n;i++)
    {
      scanf("%s",cmd);
      if(!strcmp(cmd,insert))
        {
          scanf("%d",&key);
          push_back(key);
        }
      else if(!strcmp(cmd,delete))
        {
          scanf("%d",&key);
          Delete(key);
        }
      else if(!strcmp(cmd,deleteFirst))
        {
          Delete_flont();
        }
      else if(!strcmp(cmd,deleteLast))
        {
          Delete_back();
        }
    }
    if(head->next!=NULL)
    {
        printf("%d",head->next->x);
        for(p=head->next->next;p!=NULL;p=p->next)
        {
            printf(" %d",p->x);
        }
    }
    printf("\n");
  return 0;
}