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: Time Limit Exceeded)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct node{
  int key;
  struct node *next;
  struct node *prev;
};

typedef struct node * NodePointer;

NodePointer nil;
/////////////////////////
void insert(int a){
  NodePointer n;
  n=malloc(sizeof(struct node));
  n->key=a;
  n->next=nil->next;
  nil->next->prev=n;
  n->prev=nil;
  nil->next=n;
}
/////////////////////////
void delete(int a){
  NodePointer n;
  for(n=nil->next;n!=nil;n=n->next){
    if(n->key==a)break;
  }
  n->prev->next=n->next;
  n->next->prev=n->prev;
  free(n);  
}
/////////////////////////
void deleteFirst(void){
  NodePointer n;
  n=nil->next;
  nil->next=n->next;
  n->next->prev=nil;
  free(n);
}
void deleteLast(void){
  NodePointer n;
  n=nil->prev;
  n->prev->next=nil;
  nil->prev=n->prev;
  free(n);
}
void init(void){
  nil=malloc(sizeof(struct node));
  nil->next=nil;
  nil->prev=nil;
}
int main(void){
  int i,n,key;
  char com[12];
  NodePointer k;
  scanf("%d", &n);
  init();

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

    if ( com[0] == 'i' ) {
      insert(key);

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

  }
  i=0;
  for(k=nil->next;k!=nil;k=k->next){
    if(i!=0)printf(" %d",k->key);
    else printf("%d",k->key);
    i=1;
  }
  printf("\n");
  return 0;
}