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: Accepted)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
struct node{
  int key;
  struct node *next;
  struct node *prev;
};
 
typedef struct node *NodePointer;
NodePointer N;

void init(){
  N = malloc(sizeof(struct node));
  N->next = N;
  N->prev = N;
}

void printList(){
  NodePointer cur = N->next;
  int snl = 1;
  while(cur != N){
    if ( snl == 0)  printf(" ");
    printf("%d", cur->key);
    cur = cur->next;
    snl = 0;
  }
  printf("\n");
}

void deleteFirst(){
  NodePointer t = N->next;
  N->next = t->next;
  t->next->prev = N;
}
 
void deleteLast(){
 
  NodePointer delnode = N->prev;
 
  N->prev = delnode->prev;
  delnode->prev->next = N;
  free(delnode);
}
 
void delete(int skey){
  int judge = 0;
  NodePointer t;
  NodePointer n; 

  for(n = N->next;n != N;n = n->next){
    if(n->key == skey){
      judge = 1;
    }
  }

  if(judge == 1){
    n = N->next;
    while(n != N){
      if(n->key == skey)
	break;
      n=n->next;
    }
    t = n->prev;
    t->next = n->next;
    t->next->prev = t;
    free(n);
  }
}

void insert(int skey){
  NodePointer new;
  static int count = 0;
  new = malloc(sizeof(struct node));
  new->key = skey;
 
  if(count == 0){
  new->next = N;
  N->next = new;
  new->prev = N;
  N->prev = new;
  count++;
  }
 
  else{
    new->next = N->next;
    N->next->prev = new;
    N->next = new;
    new->prev = N;
    count++;
  }
}

int main(){
  int key, n, i;
  char com[12];
   
  scanf("%d", &n);
  init();
  for ( i = 0; i < n; i++ ){
    scanf("%s",com);
    if(strcmp(com,"insert") == 0){
      scanf("%d",&key);
      insert(key);
    }
    else if(strcmp(com,"deleteFirst") == 0)
      deleteFirst();
    else if(strcmp(com,"deleteLast") == 0)
      deleteLast();
    else{
      scanf("%d",&key);
      delete(key);
    }
  }
  printList();
  return 0;
}