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

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

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;
}

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

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

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

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

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

void printList()
{
	Node *cur = nil->next;
	int isf = 0;
	while(1) {
		if(cur == nil) {
			break;
		}else {
			if(isf++ > 0)
				printf(" ");
			printf("%d", cur->key);
			cur = cur->next;
		}
	}
	printf("\n");
}

int main()
{	
	int i, n;
	int key;
	char com[15];
	scanf("%d", &n);

	init();

	for(i = 0; i < n; i++) {
		scanf("%s %d", com, &key);
		if (com[0] == 'i') {
			insert(key);
		}
		else if(com[0] == 'd') {
			if(com[6] == 'F')
				deleteFirst();
			else if(com[6] == 'L')
				deleteLast();
			else
				deleteKey(key);
		}
	}

	printList();

    return 0;
}