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>
#define LEN 13 

typedef struct _list list;
struct _list {
   int key;
   struct _list *prev, *next;
} ;

list *create_list(int key);
list *insert(int key);
void delete(int key);
void deleteFirst(void);
void deleteLast(void);
void print_list(void);
void destroy_list(void);

list *head, *tail;

int main(){
   int i, n, key;
   char cmd[LEN];
   head=NULL;
   tail=NULL;
   scanf("%d",&n);
   for(i=0;i<n;i++){
      scanf("%s %d",cmd,&key);
      if(strcmp(cmd,"insert")==0) insert(key);
      else if(strcmp(cmd,"delete")==0) delete(key);
      else if(strcmp(cmd,"deleteFirst")==0) deleteFirst();
      else if(strcmp(cmd,"deleteLast")==0) deleteLast();
//      print_list();
   }
   print_list();
   destroy_list();
   return 0;
}

list *create_list(int key){ 
   list *tmp;
   tmp=malloc(sizeof(list));
   tmp->prev=NULL;
   tmp->next=NULL;
   tmp->key=key;
   return tmp;
}

list *insert(int key){
   list *p;
   p=create_list(key);
   if(head!=NULL) head->prev=p;
   p->next=head;
   head=p;
   if(tail==NULL) tail=p;
   return p;
}

void delete(int key){
   list *p;
   p=head;
   while(p!=NULL){
      if(p->key==key){
         if(p==head) deleteFirst();
         else if(p==tail) deleteLast();
         else {
            if(p->prev!=NULL) (p->prev)->next=p->next;
            if(p->next!=NULL) (p->next)->prev=p->prev;
            free(p);
         }
         break;
      }
      p=p->next;
   }
}

void deleteFirst(void){
   list *new_head;
   if((new_head=head->next)!=NULL) new_head->prev=NULL;
   free(head);
   head=new_head;
}

void deleteLast(void){
   list *new_tail;
   if((new_tail=tail->prev)!=NULL) new_tail->next=NULL;
   free(tail);
   tail=new_tail;
}

void print_list(void){
   list *p;
   p=head;
   while(p!=NULL){
      if(p->next==NULL){
         printf("%d\n",p->key);
      } else {
         printf("%d ",p->key);
      }
      p=p->next;
   }
}

void destroy_list(void){
   while(head!=NULL){
      deleteFirst();
   }
}