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>

typedef struct node{
  struct node *prev;
  int key;
  struct node *next;
} D;

D *head;

void insert(int v);
void delete(D *v);
void find(int v);

int main()
{
  int i,n,v;
  char cmd[16];
  D *temp;
  
  head=malloc(sizeof(D));
  head->key=-1;
  head->prev=head;
  head->next=head;
  
  scanf("%d",&n);
  for(i=0;i<n;i++){
    scanf("%s",cmd);
    if(cmd[0]=='i'){
      scanf("%d",&v);
      insert(v);
    }
    else if(cmd[6]=='F') delete(head->next);
    else if(cmd[6]=='L') delete(head->prev);
    else{
      scanf("%d",&v);
      find(v);
    }
  }

  temp=head->next;
  while(temp->next->key!=-1){
    printf("%d ",temp->key);
    temp=temp->next;
  }
  if(temp->key!=-1) printf("%d\n",temp->key);
  
  return 0;
}

void insert(int v){

  D *temp;
  
  temp=malloc(sizeof(D));
  temp->key=v;
  temp->next=head->next;
  temp->prev=head;

  head->next=temp;
  temp->next->prev=temp;
}

void delete(D *v){

  v->prev->next=v->next;
  v->next->prev=v->prev;
  
  free(v);
}

void find(int v){
  
  D *temp;
  temp=head;
  
  while(temp->next->key!=-1){
    temp=temp->next;
    if(temp->key==v){
      delete(temp);
      break;
    }
  }
}