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{
  int key;
  struct Node *next, *pre;
};
typedef struct Node *NodePointer; 

NodePointer nil;

void insert( int);
void del( NodePointer t);

int main(){
  int k,n, i ,inpn=0;
  NodePointer j;
  scanf("%d",&n);
  char command[12];
  nil = ( NodePointer )malloc( sizeof( int ) + sizeof ( int *)*2);
  nil->pre =nil;  nil->next =nil;


  for ( i = 0; i < n;i++){
    scanf("%s%d" ,command , &k);
    if ( strcmp(command, "insert") == 0){ insert( k);}
    else if (  strcmp(command, "delete") == 0 ){
      for( j = nil -> next ; j != nil ;j = j-> next){
	if ( j-> key== k){break;}
      }
        del ( j); }
    else if (  strcmp(command, "deleteFirst") == 0){ del ( nil ->next) ;}
    else if (  strcmp(command, "deleteLast") == 0){  del ( nil -> pre) ;}

  }



  NodePointer nf;
  for ( nf = nil ->next ; nf != nil ; nf = nf -> next){
    printf("%d" ,nf ->key );
    if ( nf->next != nil){ printf(" ");}
  }
  
  printf("\n");
  return 0;
}


void insert ( int k){
  NodePointer x;
  x = ( NodePointer)malloc(sizeof( int ) + sizeof ( int *)*2);
  x->key = k;
  x -> next = nil -> next ;
  nil -> next -> pre = x;
  nil -> next =x;
  x -> pre =nil;
  
}


void del( NodePointer tag){
  if ( tag== nil ){return ;}
  tag -> next -> pre = tag -> pre;
  tag ->pre ->next = tag -> next;
  free(tag);
}