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: Runtime Error)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct node{
  unsigned int key;
  struct node *next;
    struct node *prev;
};
 
typedef struct node * NodePointer;

NodePointer nil;

NodePointer listSearch(int key){
 NodePointer sol = nil->next;
  while(sol->key != key && sol != nil) sol = sol->next;
  return sol;
}

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

void printList(){
  NodePointer cur = nil->next;
  int i,count = 0;

  /* int isf = 0;
  while(1){
    if(cur == nil) break;
  if(isf++ > 0) printf(" ");
   printf("%d",cur->key);
    cur = cur->next;
 }
 printf("\n");

   }
*/

  while(cur != nil->prev){
	
     printf("%d ",cur->key);
    cur = cur->next;
    if(cur == nil) break;//return;
  }
   printf("%d\n", cur->key);
 }
 
 
 void deleteNode(NodePointer t){
   t->prev->next = t->next;
   t->next->prev = t->prev;
   free(t);
 }
 
 void deleteFirst(){
   NodePointer t = nil->next;
   if ( t == nil ) return;
   deleteNode(t);
  }
 
 void deleteLast(){
   NodePointer t;
   t = nil->prev;
   if(t == nil) return;
   deleteNode(t);
  }
 
 void delete(int key){
    deleteNode(listSearch(key));
  }
 
 
 void insert(int key){
   NodePointer x;
   x = malloc(sizeof(struct node));
   x->key = key;
   x->next = nil->next;
   x->next->prev = x;
   nil->next = x;
   x->prev = nil;
 
 }
 
NodePointer listSearch(int key);
 void init();
 void printList();
 void deleteNode(NodePointer t);
 void deleteFirst();
 void deleteLast();
 
 
int main(){
   int key, n, i;
   int size = 0;
   char com[20];
   int np = 0, nd = 0;
  scanf("%d", &n);
  init();
  for ( i = 0; i < n; i++ ){
    scanf("%s%d", com, &key);
    if ( com[0] == 'i' ) {insert(key); np++; size++;}
    else if ( com[0] == 'd' ) {
     if (strlen(com) > 6){
        if ( com[6] == 'F' ) deleteFirst();
        else if ( com[6] == 'L' ) deleteLast();
      } else {
        delete(key);
        nd++;
      }
      size--;
    }
  }

  printList();
  return 0;
}