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>

struct node{

  unsigned int key;
  struct node *next;
  struct node *prev;

};

typedef struct node *NodePointer;

NodePointer nil;


NodePointer listSearch(int key)
{
  NodePointer n;

  for( n=nil->next; n != nil; n=n->next )
    {
      if( n->key == key ) return n;
    }
  return nil;
}


void initial()
{
  nil = malloc(sizeof(struct node));
  nil->next = nil;
  nil->prev = nil;
}


void printList()
{
  NodePointer cur = nil->next;
  int isf = 1;

  while(1)
    {
      if( cur == nil ) break;
      if( isf == 0 ) printf(" ");
      printf("%d", cur->key);
      cur = cur->next;
      isf = 0;
    }
  printf("\n");
}


void deleteNode(NodePointer t)
{
  t->prev->next = t->next;
  t->next->prev = t->prev;
  free(t);
}


void deleteFirst()
{
  NodePointer t = nil->next;
  
  if( t == nil ) return;
  deleteNode(t);
}


void deleteLast()
{
  NodePointer t = nil->prev;

  if( t == nil ) return;
  deleteNode(t);
 
}


void delete(int key)
{
  NodePointer x;

  if( (x = listSearch(key)) == nil ) return;
  
  x->prev->next = x->next;
  x->next->prev = x->prev;
  free(x);
}

void insert(int key)
{
  NodePointer x;
  
  x = malloc(sizeof(struct node));
  x->key = key;
  x->next = nil->next;
  nil->next->prev = x;
  nil->next = x;
  x->prev = nil;
}

int main()
{
  int key, n, i;
  int size = 0;
  char command[20];
  int np = 0, nd = 0;

  scanf("%d", &n);
  initial();

  for( i=0; i<n; i++ )
    {
      scanf("%s%d", command, &key);

      if( command[0] == 'i' )
	{
	  insert(key);
	  np++;
	  size++;
	}

      else if( command[0] == 'd' )
	{
	  if( strlen(command) > 6 )
	    {
	      if( command[6] == 'F' ) deleteFirst();
	      else if( command[6] == 'L' ) deleteLast();
	    }

	  else
	    {
	      delete(key);
	      nd++;
	    }
	  
	  size--;
	}
    }

  printList();

  return 0;
}