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

void init()
{
  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;
}

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 t;
  if(listSearch(key) == NULL)
    {
      return;
    }
  t = listSearch(key);
  deleteNode(t);
}

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 com[20];
  int np = 0,nd = 0;
  scanf("%d",&n);
  init();
  for(i = 0;i < n;i++)
    {
      scanf("%s",com);
      if(com[0] == 'i')
	{
	  scanf("%d",&key);
	  insert(key);
	  np++;
	  size++;
	}
      else if (com[0] == 'd')
	{
	  if(strlen(com) > 6)
	    {
	      if(com[6] == 'F')
		{
		  deleteFirst();
		}
	      else if(com[6] == 'L')
		{
		  deleteLast();
		}
	    }
	  else
	    {
	      scanf("%d",&key);
	      delete(key);
	      nd++;
	    }
	  size--;
	}
    }
  printList();
  return 0;
}