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>

typedef int MYDATA;

struct CELL{
	struct CELL* prev;
	struct CELL* next;
	MYDATA value;
};

struct CELL head;

void init();
void insertFirst(MYDATA x);
void insertLast(MYDATA x);
void delete(MYDATA x);
void deleteFirst();
void deleteLast();
void deleteAll();

int main(void){
	struct CELL *p;
	int i,n;
	char s[20];
	MYDATA data;

	init();

	scanf("%d",&n);

	for(i=0;i<n;i++){
		scanf("%s",s);
		if(!strcmp(s,"insert")){
				scanf("%d",&data);
				insertFirst(data);
		}else if(!strcmp(s,"delete")){
				scanf("%d",&data);
				delete(data);
		}else if(!strcmp(s,"deleteFirst")){
				deleteFirst();
		}else if(!strcmp(s,"deleteLast")){
				deleteLast();
		}
	}

	for(p = head.next;p != (&head)->prev; p = p->next)
		printf("%d ", p->value);

	
	printf("%d\n", p->value);

	return 0;
}

void init(){
	head.prev = head.next = &head;
}

void insertFirst(MYDATA x){
	struct CELL *temp;

	temp=(struct CELL*)malloc(sizeof(struct CELL));

	temp->value = x;
	temp->prev = &head;
	temp->next = head.next;
	(&head)->next->prev = temp;
	head.next = temp;
}

void insertLast(MYDATA x){
	struct CELL *temp;

	temp=(struct CELL*)malloc(sizeof(struct CELL));

	temp->value = x;
	temp->prev = head.prev;
	temp->next = &head;
	(&head)->prev->next = temp;
	head.prev = temp;
}

void delete(MYDATA x){
	struct CELL *p;

	for(p = head.next;p != &head; p = p->next){
		if(p->value==x){
			p->prev->next = p->next;
			p->next->prev = p->prev;
			break;
		}
	}
}

void deleteFirst(){
	(&head)->next = (&head)->next->next;
	(&head)->next->prev = &head;
}

void deleteLast(){
	(&head)->prev = (&head)->prev->prev;
	(&head)->prev->next = &head;
}

void deleteAll(){
	init();
}