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

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

  return 0;
}
 
void insert(int key){
    NodePointer x;
    x=malloc(sizeof(struct node));
    x->key=key;
    x->next=nil.next;
    x->prev=&nil;
    nil.next=x;
    x->next->prev=x;
}
 
int delete(int key){
  NodePointer p;
  p=nil.next;
  while(p!=NULL&&p->key!=key){
    p=p->next;
  }
  if(p==NULL){
    return 0;
  }else{
    p->prev->next=p->next;
    p->next->prev=p->prev;
    free(p);
    return 0;
  }
}
 
int deleteFirst(){
    NodePointer p,q;
    p=nil.next;
    q=&nil;
    p->next->prev=q;
    nil.next=p->next;
    free(p);
    return 0;
}
 
int deleteLast(){
    NodePointer p;
    p=nil.prev;
    p->prev->next=&nil;
    nil.prev=p->prev;
    free(p);
    return 0;
}