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

typedef struct _node
{
	int value;
	struct _node * next;
	struct _node * prev;
} node_t;

node_t *head;
node_t *p;


void Init()
{
//	fprintf( stdout, "init finished\n" );
	head = malloc( sizeof( node_t ) );
	head->next = NULL;
	head->prev = NULL;
	head->value = 100;
	p = head;
}

void Insert( int x )
{
//	fprintf( stdout, "insert started\n" );
	node_t *newnode;
	newnode = malloc( sizeof( node_t ) );
	p->next = newnode;
	newnode->value = x;
	newnode->next = NULL;
	newnode->prev = p;
	p = newnode;
}

void Delete( int x )
{
	node_t *pointer;
	pointer = p;

	while ( pointer != NULL )
	{
		if( pointer->value == x )
		{
			if ( pointer == p )
			{
				pointer->prev->next = NULL;
				p = pointer->prev;
			}
			else 
			{
				pointer->prev->next = pointer->next;
				pointer->next->prev = pointer->prev;
			}	
			free( pointer );
			break;
		}
		pointer = pointer->prev;
	}
}

void DeleteLast()
{
	node_t *pointer;

	if ( head->next == NULL )
	{
		;
	}
	else
	{
		pointer = head->next;
		if ( pointer->next != NULL )
		{
			head->next = pointer->next;
			pointer->next->prev = head;
		}
		else
		{
			p = head;
		}
		free( pointer );
	}
}


void DeleteFirst()
{
	node_t *pointer;
	pointer = p;
	if ( pointer == head )
	{
		;
	}
	else
	{
		p = pointer->prev;
		free( pointer );
		p->next = NULL;
	}
}

void PrintValue()
{
	node_t *pointer;
	pointer = p;

	while( pointer != head )
	{
		if ( pointer->prev == head )
		{
			fprintf( stdout, "%d", pointer->value );
		}
		else
		{
			fprintf( stdout, "%d ", pointer->value );
		}
		pointer = pointer->prev; 
	}

	fprintf( stdout, "\n");
}

int main()
{
	int n, i = 0, num;
	char s[12];

	Init();

	scanf( "%d", &n );
	while ( i < n )
	{
		scanf( "%s", s );
		if ( strcmp( s, "insert" ) == 0 )
		{
			scanf( "%d", &num );
			Insert( num );
		}
		else if ( strcmp( s, "delete" ) == 0 )
		{
			scanf( "%d", &num );
			Delete( num );
		}
		else if ( strcmp( s, "deleteFirst" ) == 0 )
		{
			DeleteFirst();
		}
		else if ( strcmp( s, "deleteLast" ) == 0 )
		{
			DeleteLast();
		}
	//	PrintValue();
		i = i + 1;
	}

	PrintValue();

	return 0;
}