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)

//Doubly Linked List

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define N 20

typedef struct Node
{
  int key;
  struct Node *n,*p;
  
}Node;

Node *nil;

void initialize()
{
  nil = (Node *)malloc(sizeof(Node));
  nil -> n = nil;
  nil -> p = nil;
}

Node* search(int key)
{
  Node *now = nil->n;

  while(now != nil && now->key != key)
    {
      now = now->n;
    }
  return now;
}

void delete(Node *x)
{
  if(x == nil) return;
  x->p->n = x->n;
  x->n->p = x->p;
  free(x);
}

void deleteF()
{
  delete(nil -> n);
}

void deleteL()
{
  delete(nil -> p);
}

void deleteK(int key)
{
  delete(search(key));
}

void insert(int key)
{
  Node *x = (Node *)malloc(sizeof(Node));
  x->key = key;
  x->n = nil-> n;
  nil->n->p = x;
  nil->n = x;
  x->p = nil;
}

void print()
{
  int imp = 0;
  Node *now = nil -> n;

  while(1)
    {
      if(now == nil) break;
      if(imp ++ > 0) printf(" ");
      printf("%d",now->key);
      now = now->n;
    }
  printf("\n");
}

int main()
{
  int i,n,key;
  int size = 0,a = 0, b = 0;
  char arr[N];

  //input & initialize data
  scanf("%d",&n);
  initialize();
  for(i = 0; i < n; i++)
    {
      scanf("%s%d",arr,&key);

      //work
      if(arr[0] == 'i')
	{
	  insert(key);
	  a++;
	  size++;
	}
      else if(arr[0] == 'd')
	{
	  if(strlen(arr) > 6)
	    {
	      if(arr[6] == 'F') deleteF();
	      else if(arr[6] == 'L') deleteL();
	    }else{
	    deleteK(key);
	    b++;
	  }
	  size--;
	}
    }

  //output data
  print();

  return 0;
  
}