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 <malloc.h>
#include <string.h>
struct node{
  struct node *next;
  struct node *prev;
  int key;
};
typedef struct node * NodePointer;
struct node nil;
int flag=0;
NodePointer f;

void insert(int);
void delete(int);
void deleteFirst(void);
void deleteLast(void);
void init(){
	nil.next=NULL;
	nil.prev=NULL;
}

int main(){
	NodePointer p;
	int i, n, key;
	char com[12];
	scanf("%d", &n);
	init();
	for ( i = 0; i < n; i++ ){
		scanf("%s",com);
		if(strlen(com)>6){
			if(com[6]=='F'){
				deleteFirst();
			} else if ( com[6] == 'L' ) {
				deleteLast();
			} 
		}else{
			scanf("%d",&key);
			if(com[0]=='i'){
				insert(key);
			}else{
      		delete(key);
       }
    }
	}
  for(p=nil.next;flag>1;p=p->next,flag--){
    printf("%d ",p->key);
  }
  printf("%d\n",p->key);
  return 0;
}


void insert(int key){
	NodePointer temp;
	flag++;
	temp=(NodePointer)malloc(sizeof(struct node));
	if(flag==1)f=temp;
	temp->key=key;
	temp->next=nil.next;
	temp->prev=&nil;
	nil.next=temp;
	if(flag>1)temp->next->prev=temp;
}

void delete(int key){
	NodePointer p, q;
	p=nil.next;
	q=&nil;
	while(p!=NULL&&p->key!=key){
		q = p;           /*This q have prevew of p*/
    p = p->next;
	}
	if(p==f){
		deleteLast();
	}else if(p!=NULL){
 		q->next=p->next;
		p->next->prev=p;
		free(p);
		flag--;
	}
}

void deleteFirst(){
	NodePointer p, q;
	p=nil.next;
	q=&nil;
	q->next=p->next;
	p->next->prev=q;
	free(p);
	flag--;
}

void deleteLast(){
	NodePointer p,q;
	p=f;
	f=f->prev;
	free(p);
	flag--;
}