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 <string.h>
#include <stdlib.h>
typedef struct node *link;

struct node{
  int item;
  link next, prev;
};

int main(void){
  int n, i, j, getitem, size = 0;
  char s[256];
  link head;
  head = malloc(sizeof(*head));
  head->item = -1;
  head->next = NULL;
  head->prev = NULL;
  
  scanf("%d", &n);
  
  for(i = 0; i < n; i++){
    scanf("%s", s);
    if(!strcmp(s, "insert")){ //insert
      scanf("%d", &getitem);
      link x;
      x = malloc(sizeof(*x));
      x->item = getitem;
      x->next = head;
      x->prev = NULL;
      head->prev = x;
      head = x;
      size++;
    }else if(!strcmp(s, "delete")){ //delete
      scanf("%d", &getitem);
      link x;
      x = malloc(sizeof(*x));
      x = head;
      if(head->item == getitem){
	head = head->next;
	head->prev = NULL;
	size--;
	continue;
      }
      while(x->next->item != -1){
	if(x->next->item == getitem){
	  x->next = x->next->next;
	  x->next->prev = x;
	  size--;
	  break;
	}else{
	  x = x->next;
	}
      }
    }else if(!strcmp(s, "deleteFirst")){ //deleteFirst
      if(size == 0){
	continue;
      }
      head = head->next;
      head->prev = NULL;
      size--;
    }else if(!strcmp(s, "deleteLast")){ //deleteLast
      if(size == 0){
	continue;
      }else if(size == 1){
	head = head->next;
	head->prev = NULL;
	size--;
	continue;
      }
      link x;
      x = malloc(sizeof(*x));
      x = head;
      for(j = 0; j < size-2; j++){
	x = x->next;
      }
      x->next = x->next->next;
      x->next->prev = x;
      size--;
    }
  }

  
  link x;
  x = malloc(sizeof(*x));
  x = head;
  while(!(x->next == NULL)){
    printf("%d", x->item);
    if(x->next->item == -1) break;
    printf(" ");
    x = x->next;
  }
  
  printf("\n");
  return 0;
}