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 <string.h>
#include <stdlib.h>

struct NODE {
	int key;
	struct NODE *pre;
	struct NODE *next;
};

struct NODE *InsertFirst(struct NODE *node, const int x);
struct NODE *DeleteX(struct NODE *node, const int x);
struct NODE *DeleteFirst(struct NODE *node);
struct NODE *DeleteLast(struct NODE *node);
void PrintList(struct NODE *p);

int main(void) {
	struct NODE *head;

	head = NULL;

	int n;
	char order[20];
	int keynum;
	int i;

	scanf("%d", &n);

	for (i = 0; i < n;i++) {
		scanf("%s" ,order);

		if (strcmp(order, "insert") == 0) {
			scanf("%d", &keynum);
			head = InsertFirst(head, keynum);
		}
		else if (strcmp(order, "delete") == 0) {
			scanf("%d", &keynum);
			head = DeleteX(head, keynum);
		}
		else if (strcmp(order, "deleteFirst") == 0) {
			head = DeleteFirst(head);
		}
		else if (strcmp(order, "deleteLast") == 0) {
			head = DeleteLast(head);
		}
	}

	struct NODE *p;
	p = head;

	PrintList(head);

	return 0;
}

struct NODE *InsertFirst(struct NODE *head, const int x) {
	struct NODE *p;

	if ((p = (struct NODE *)malloc(sizeof(struct NODE))) == NULL) {
		printf("malloc error:データの追加に失敗しました。\n");
		exit(1);
	}

	p->key = x;
	p->next = head;
	if (head != NULL) {
		head->pre = p;
	}
	head = p;

	return head;
}

struct NODE *DeleteX(struct NODE *head, const int x) {
	if (head != NULL) {
		if (head->next == NULL) {
			head = NULL;
			free(head);
		}
		else if (head->key == x) {
			struct NODE *p;
			p = head->next;
			p->pre = NULL;
			free(head);
			head = p;
		}
		else {
			struct NODE *p;
			p = head->next;
			while (p->key != x) {
				p = p->next;
				if (p == NULL) {
					return head;
				}
			}
			if (p->next == NULL) {
				p->pre->next = NULL;
			}
			else {
				p->pre->next = p->next;
				p->next->pre = p->pre;
			}
			free(p);
		}
	}

	return head;
}

struct NODE *DeleteFirst(struct NODE *head) {
	head = DeleteX(head, head->key);
	return head;
}

struct NODE *DeleteLast(struct NODE *head) {
	if (head != NULL) {
		if (head->next == NULL) {
			head = NULL;
			free(head);
		}
		else {
			struct NODE *p;
			struct NODE *pre_p;
			p = head->next;
			pre_p = head;
			while (p->next != NULL) {
				pre_p = p;
				p = p->next;
			}
			pre_p->next = NULL;
			free(p);
		}
	}

	return head;
}

void PrintList(struct NODE *p) {

	while (p != NULL) {
		printf("%d", p->key);
		p = p->next;

		if (p != NULL) {
			printf(" ");
		}
	}

	printf("\n");
}