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<stdio.h>
#include<stdlib.h>
#include<string.h>
 
typedef struct Node
{
  int key;
  struct Node *next,*prev;
}Node;
 
Node *nl;
 
Node* listSearch(int key)
{
  Node *cu=nl->next;
  while(cu!=nl && cu->key !=key)
    {
      cu=cu->next;
    }
  return cu;
}
 
void init()
{
  nl=(Node *)malloc(sizeof(Node));
  nl->next=nl;
  nl->prev=nl;
}
 
void printlist()
{
  Node*cu=nl->next;
  int f=0;
  while(1)
    {
      if(cu==nl) break;
      if(f++>0)printf(" ");
      printf("%d",cu->key);
      cu=cu->next;
    }
  printf("\n");
}
 
void deleteNode(Node *r)
{
  if(r==nl)return;
  r->prev->next=r->next;
  r->next->prev=r->prev;
  free(r);
}
 
void deletefirst()
{
  deleteNode(nl->next);
}
 
void deletelast()
{
  deleteNode(nl->prev);
}
 
void deletekey(int key)
{
  deleteNode(listSearch(key));
}
 
void insert(int key)
{
  Node *a=(Node *)malloc(sizeof(Node));
  a->key=key;
  a->next=nl->next;
  nl->next->prev=a;
  nl->next=a;
  a->prev=nl;
}
 
int main()
{
  int key,i,n;
  int cnt=0;
  char order[20];
  int p=0,d=0;
  scanf("%d",&n);
  init();
  for(i=0;i<n;i++)
    {
      scanf("%s%d",order,&key);
      if(order[0]=='i')
    {
      insert(key);
      p++;
      cnt++;
    }
      else if(order[0]=='d')
    {
      if(strlen(order)>6)
        {
          if(order[6]=='F') deletefirst();
          else if(order[6]=='L')deletelast();
        }
      else
        {
        deletekey(key);
        d++;
        }
      cnt--;
    }
    }
  printlist();
  return 0;
}