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>
struct node
{
    int key;
    struct node *next, *prev;
};
struct node *nil; 
void init()
{
    nil=(struct node *)malloc(sizeof(struct node));
    nil->next=nil;
    nil->prev=nil;
} 
struct node *listSearch(int keys)
{
    struct node *cur=nil->next;
    while(cur!=nil && cur->key!=keys)
        cur=cur->next; 
    return cur;
} 
void insert(int keys)
{
    struct node *x=(struct node *)malloc(sizeof(struct node));
    x->key=keys;
    //insert
    x->next=nil->next;
    nil->next->prev=x;
    nil->next=x;
    x->prev=nil;
} 
void Delete(struct node *t)
{
    if(t==nil) return;
    t->prev->next=t->next;
    t->next->prev=t->prev;
    free(t);
} 
void deleteFirst()
{
    Delete(nil->next);
} 
void deleteLast()
{
    Delete(nil->prev);
} 
void printList()
{
    struct node *cur=nil->next;
    while(cur->next != nil)
    {
        printf("%d ", cur->key);
        cur=cur->next;
    }
    printf("%d\n", cur->key);
}
int main()
{
    int n, x,i;
    char comm[12];
 
    scanf("%d", &n);
 
    init();
 
    for(i=0; i<n; i++)
    {
        scanf("%s", comm);
        if(comm[0]=='i')
        {
            scanf("%d", &x);
            insert(x);
        }
        if(comm[0]=='d')
        {
            if(comm[6]=='F') deleteFirst();
            else if(comm[6]=='L') deleteLast();
            else
            {
                scanf("%d", &x);
                Delete(listSearch(x));
            }
        }
    }
    printList(); 
    return 0;
}