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>
#include<string.h>

/*要素の構造*/
struct node {
	unsigned int key;
	struct node *next;
	struct node *prev;
};

/*要素のポインタ*/
typedef struct node * NodePointer;

/*最初、最後のポインタ*/
NodePointer nil;

/*指定されたキーを持った要素を探す*/
NodePointer listSearch(int key) {
	NodePointer x;
	x = nil->next;

	/*リストの最初から最後まで探していく*/
	while (x != nil->prev) {
		/*キーが一致したらポインタを返す*/
		if (x->key == key) {
			return x;
			break;
		}
		x = x->prev;
	}

	/*見つからなかったとき*/
	return nil;
}

/*リストの最初と最後の初期化*/
void init() {
	nil = malloc(sizeof(struct node));
	nil->next = nil;	/*リストの最初*/
	nil->prev = nil;	/*リストの最後*/
}

/*出力*/
void printList() {
	NodePointer cur = nil->next;
	int isf = 1;
	while (1) {
		if (cur == nil) {
			break;
		}
		/*最初の要素以外はスペースを前に付ける*/
		if (isf == 0) {
			printf(" ");
		}
		printf("%d", cur->key);
		cur = cur->next;
		free(cur->prev);
		isf = 0;
	}
	printf("\n");
}

/*指定された要素を削除*/
void deleteNode(NodePointer t) {
	NodePointer x;
	x = t->prev->next;
	t->prev->next = t->next->prev;
	t->next->prev = x;
	free(t);
}

/*最初の要素を削除*/
void deleteFirst() {
	NodePointer t = nil->next;
	if (t == nil) {
		return;
	}
	deleteNode(t);
}

/*最後の要素を削除*/
void deleteLast() {
	NodePointer t = nil->prev;
	if (t == nil) {
		return;
	}
	deleteNode(t);
}

/*指定されたキーを持つ要素を削除*/
void delete(int key) {
	NodePointer x;
	x = listSearch(key);
	if (x != nil) {
		deleteNode(x);
	}
	else {
		return;
	}
}

/*要素の追加*/
void insert(int key) {
	NodePointer x;
	x = malloc(sizeof(struct node));

	x->key = key;

	/*リストにすでに要素があるとき*/
	if (nil->next != nil) {
		/*先頭の要素のポインタを書き換える*/
		nil->next->next = x;
		x->prev = nil->next;
	}
	else {
		nil->prev = x;
	}
	x->next = nil;
	nil->next = x;
}

int main() {
	int key, n, i;		/*入力されるキー、命令数、ソート用変数*/
	int size = 0;		/*リストの要素数*/
	char com[20];		/*命令文字列*/
	int np = 0, nd = 0;	/*継ぎ足しと削除の回数*/

	/*命令数の取得*/
	scanf("%d", &n);

	/*リストの初期化*/
	init();

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

	printList();
	return 0;
}