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 struct node {
	int key;
	struct node *next;
	struct node *prev;
} Node;

Node *nil;

void init()
{
	nil = (Node *)malloc(sizeof(Node));
	nil->next = nil;
	nil->prev = nil;
}

Node* listSearch(int key)
{
	Node *cur = nil->next;
	while (cur != nil && cur->key != key) {
		cur = cur->next;
	}
	return cur;
}

void deleteNode(Node *x)
{
	if (x == nil) return;
	x->prev->next = x->next;
	x->next->prev = x->prev;
	free(x);
}

void delete(int key)
{
	deleteNode(listSearch(key));
}

void deleteFirst()
{
	deleteNode(nil->next);
}

void deleteLast()
{
	deleteNode(nil->prev);
}

void insert(int key)
{
	Node *x = (Node *)malloc(sizeof(Node));
	x->key = key;
	x->next = nil->next;
	nil->next->prev = x;
	nil->next = x;
	x->prev = nil;
}

void print_node()
{
	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 com[100];
	init();
	scanf("%d", &n);
	for (i = 0; i < n; i++) {
		scanf("%s %d", com, &x);
		if (com[0] == 'i')
			insert(x);
		else if (com[0] = 'd') {
			if (strlen(com) > 6) {
				if (com[6] == 'F') {
					deleteFirst();
				}
				else if (com[6] == 'L') {
					deleteLast();
				}
			}
			else
				delete(x);
		}
	}
	print_node();
	return 0;
}