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 num;
  struct node *prev;
  struct node *next;
};
   
typedef struct node *NodePointer;
 
 
NodePointer make1node(NodePointer,int);
void showlist();
void insert(int);
void delete(int);
void deletefirst();
void deletelast();
 
NodePointer head;
 
int main(){
  int i, cou, num;
  char str[10];
   
 
  head = make1node(NULL, 0);
  head->next = head;
  head->prev = head;
  scanf("%d", &cou);
 
   
  for (i = 0; i < cou; i ++){
    scanf("%s", str);
     
    if(strcmp(str, "insert") == 0){
      scanf("%d", &num);
      insert(num);
    }
    if(strcmp(str, "delete") == 0){
      scanf("%d", &num);
      delete(num);
    }
    if(strcmp(str, "deleteFirst") == 0){
      deletefirst();
    }
    if(strcmp(str, "deleteLast") == 0){
      deletelast();
    }
  }
  showlist();
  return 0;
}
 
NodePointer make1node(NodePointer p, int num){
  NodePointer n;
   
  n = (NodePointer)malloc(sizeof(struct node));
  n->next = p;
  n->num = num;
 
  return n;
}
 
void showlist(){
  NodePointer n;
 
  n = head->next;
  while(n->next != head){
    printf("%d ",n->num);
    n = n->next;
  }
  printf("%d\n",n->num);
}
 
void insert(int num){
  NodePointer new;
  new = make1node(NULL, num);
  new->next = head->next;
  head->next->prev = new;
  head->next = new;
  new->prev = head;
}
 
void delete(int num){
  NodePointer n;
  /*
  for (n = head; n->next != NULL; n = n->next) {
    if (n->next->num == num){
      del = n->next;
      n->next = del->next;
      free(del);
      return n;
    }
  }
  return NULL;
  */
 
  n = head->next;
  while(n != head && n->num != num){
    n = n->next;
  }
  if(n != head){
    n->prev->next = n->next;
    n->next->prev = n->prev;
    free(n);
  }
}
 
void deletefirst(){
  NodePointer n;
 
  n = head->next;
  n->prev->next = n->next;
  n->next->prev = n->prev;
  free(n);
}
 
void deletelast(){
  NodePointer n, del;
 
  n = head->prev;
  n->prev->next = n->next;
  n->next->prev = n->prev;
  free(n);
}