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>
typedef struct node{
  int key;
  struct node *prev;
  struct node *next;
}Node, *NodePointer;
 
 
 
NodePointer nil;
 
void init(){
  nil = malloc(sizeof(Node));
  nil->next = nil;
  nil->prev = nil;
}
 
void insert(int key){
  
  NodePointer x = malloc(sizeof(Node));

  x->key = key;
  x->next = nil->next;

  nil->next->prev = x;
  nil->next = x;
  x->prev = nil;
}



NodePointer listSearch(int key){
  NodePointer s;
  s = nil->next;

  while(s != nil && s->key != key){
    s = s->next;
  }
  
  return s;
}
 
void deleteNode(NodePointer d){
  if(d == nil)return;
 
  d->prev->next = d->next;
  d->next->prev = d->prev;
  free(d);
}
 
void deleteKey(int key){
  deleteNode(listSearch(key));
}
void deleteFirst(){
  deleteNode(nil->next);
}
 
void deleteLast(){
  deleteNode(nil->prev);
}
 
void printlist(){
  NodePointer p = nil->next;
  while(1){
    if(p == nil)break;
    printf("%d",p->key);
    if(p->next != nil){
      printf(" ");
    }
    p = p->next;
  }
  printf("\n");
}
 
int main(){
  int n, key,i;
  char com[11];
 
  scanf("%d",&n);
 
  init();
  for(i=0;i<n;i++){
    scanf("%s%d",com,&key);
 
    if(com[0] == 'i'){
      insert(key);
    }
    else if(com[0] == 'd'){
      if(com[6] == 'F'){
        deleteFirst();
      }
      else if(com[6] == 'L'){
        deleteLast();
      }
      else{
        deleteKey(key);
      }
    }
 
  }
   printlist();
  return 0;
}