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 *Node;
Node head;
void delete(Node);
int main(){
  int n,i,flag,key;
  char inst[12];
  Node index;
  scanf("%d",&n);
  head = (Node *)malloc(sizeof(Node));
  head->next = head;
  head->prev = head;
  for(i=0;i<n;i++){
    scanf("%s",inst);
    if( strcmp(inst,"deleteFirst") == 0 ){
      delete(head->next);
    }
    else if( strcmp(inst,"deleteLast") == 0){
      delete(head->prev);
    }
    else{
      scanf("%d",&key);
      if( strcmp(inst,"insert") == 0){
	Node tmp;
	tmp = (Node *)malloc(sizeof(Node));
	tmp->key = key;
	tmp->next = head->next;
	head->next->prev = tmp;
	head->next = tmp;
	tmp->prev = head;
      }
      else{
	index = (Node *)malloc(sizeof(Node));
	index = head->next;
	while( index != head && index->key != key){
	  index = index->next;
	}
	if( index == head ){
	  continue;
	}
	delete(index);
      }
    }
  }
  index = head->next;
  flag = 0;
  while(index != head){
    if( flag > 0){
      printf(" ");
    }
    flag++;
    printf("%d",index->key);
    index = index->next;
  }
  printf("\n"); 
  return 0;
}
void delete(Node tmp){
  tmp->next->prev = tmp->prev;
  tmp->prev->next = tmp->next;
  free(tmp);
}