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>

int a[2000010];
int l,r;

int main(){
	int n;
	scanf("%d",&n);
	while(n--){
		char s[99];
		scanf("%s",s);
		if(s[0]=='i')scanf("%d",a+r++);
		else if(s[6]==0){
			int t;
			scanf("%d",&t);
			for(int idx=r-1;idx>=l;idx--)if(a[idx]==t){
				a[idx]=-1;
				break;
			}
		}else if(s[6]=='F')while(a[--r]==-1);
		else while(a[l++]==-1);	
	}
	int f=0;
	for(int i=r-1;i>=l;i--)if(a[i]!=-1)printf(f++?" %d":"%d",a[i]);
	puts("");
}