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>

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

void insert(int);
void delete(int);
void deleteFirst();
void deleteLast();

struct list nil={NULL,&nil,&nil};

int main(){
  int i,n,num;
  char order[12];
  struct list* x;

  scanf("%d",&n);

  for(i=0;i<n;i++){
    scanf("%s",order);

    if(strcmp(order,"insert")==0){
      scanf("%d",&num);
      insert(num);
    }

    else if(strcmp(order,"delete")==0){
      scanf("%d",&num);
      delete(num);
    }

    else if(strcmp(order,"deleteFirst")==0) deleteFirst();
    else deleteLast();
  }

  x=nil.next;
  while(x->next!=&nil){
    printf("%d ",x->key);
    x=x->next;
  }
  printf("%d\n",x->key);

  return 0;
}

void insert(int k){
  struct list* x=(struct list*)malloc(sizeof(struct list));
  x->key=k;

  x->next=nil.next;
  nil.next->prev=x;
  nil.next=x;
  x->prev=&nil;
}

void delete(int k){
  struct list* x=nil.next;

  while(x!=&nil&&x->key!=k) x=x->next;

  if(x->key==k){
    x->prev->next=x->next;
    x->next->prev=x->prev;
  }
}

void deleteFirst(){
  struct list* x=nil.next;
  
  x->prev->next=x->next;
  x->next->prev=x->prev;
}

void deleteLast(){
  struct list* x=nil.next;

  while(x->next!=&nil) x=x->next;

  x->prev->next=x->next;
  x->next->prev=x->prev;
}