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>

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

struct Node *nil;

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

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

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


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

int main()
{
	int key,n,i;
	char com[20];
	nil = (struct Node*)malloc(sizeof(struct Node));
	nil->next = nil;
	nil->prev = nil;
	
	scanf("%d",&n);

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