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>


typedef struct node {long int item; struct node *next;} link;


link *insert(link *nxt,long int item){
 link *A;
 A =malloc(sizeof(link));
 A->item = item;
 A-> next =nxt;
 return A;
}


link *deleteFirst(link *B){
 link *A;
 A=B->next;
 free(B);
 return A;
}


link *delete(link *B,long int key){
 link *A,*C;
 A=B;
 C=B;
 if(B->item == key){
 B=deleteFirst(B);
 C=B;
}else{
 while(B ->next != NULL && B->item != key){  
 A=B; 
 B = B ->next;
 }
 
 if (B->item==key){
 A->next=A->next->next;
 free(B);
}}
 return C;
}


link *deleteLast(link *B){
 link *A,*C;
 C = B;
 if(B->next ==NULL) return NULL;
 while(B->next != NULL){
 A=B;
 B = B->next;
 }
 A->next = NULL;
 free(B);
 return C;
}

int main(void){
int n;
long int B;
char A[50];
char *s1 = "insert";
char *s2 = "delete";
char *s3 = "deleteFirst";
char *s4 = "deleteLast";

link *head;
 head =NULL;


scanf("%d",&n);

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

 if(strcmp(s1,A)==0){
 scanf("%ld",&B);
  head=insert(head,B);
 }
 if(strcmp(s2,A)==0){
  scanf("%ld",&B);
  head=delete(head,B);
 }
 if(strcmp(s3,A)==0){
  head=deleteFirst(head);
 }
 if(strcmp(s4,A)==0){
  head=deleteLast(head);
 }
}


printf ("%ld",head->item);
link *First;
First = head->next;

while(First !=NULL){
 printf(" %ld",First->item);
 First = First->next;
}
 printf("\n");
return 0;
}