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: Time Limit Exceeded)

#include <stdio.h>
#include <stdlib.h>
struct dll_t {
	int key;
	struct dll_t *next;
};
typedef struct dll_t List;

List *insert(List *head, int value) {
	List *p;

	p = head;
	head = (List*)malloc(sizeof(List));
	head->next = p;
	head->key = value;
	return head;
}

List *delete(List *head, int value) {
	List *p, *prev = NULL;

	if (value == -1) {
		p = head;
	} else if (value == -2) {
		for (p = head; p->next != NULL; p = p->next) {
			prev = p;
		}
	} else {
		for (p = head; p != NULL; p = p->next) {
			if (p->key == value)
				break;
			prev = p;
		}
	}
	if (p != NULL) {
		if (p == head) {
			head = head->next;
		}
		if (prev != NULL) {
			prev->next = p->next;
		}
	}
	free(p);
	return head;
}

int main(void) {
	int n, value;
	char cmd[15];
	struct dll_t *p = NULL, *first = NULL;
	const char *fmt;

	scanf("%d ", &n);
	while (n--) {
		scanf(" %s ", cmd);
		if (cmd[0] == 'i') {
			scanf(" %d ", &value);
			first = insert(first, value);
		} else if (cmd[0] == 'd') {
			if (cmd[6] == '\0') {
				scanf(" %d ", &value);
				first = delete(first, value);
			} else if (cmd[6] == 'F') {
				first = delete(first, -1);
			} else if (cmd[6] == 'L') {
				first = delete(first, -2);
			}
		}
	}
	fmt = "%d";
	for (p = first; p != NULL;) {
		printf(fmt, p->key);
		first = p;
		p = p->next;
		free(first);
		fmt = " %d";
	}
	putchar('\n');
	return 0;
}