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{
	unsigned int key;
	struct node *next;
	struct node *prev;
};

typedef struct node * NodePointer;

NodePointer nil;

NodePointer listSearch( int key )
{
	NodePointer cur = nil->next;
	while( 1 ) {
		if( cur == nil ) { break; }
		if( cur->key == key ) { break; }
		cur = cur->next;
	}
	return cur;
}

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

void printList( )
{
	NodePointer cur = nil->next;
	int isf = 1;
	while(1) {
		if( cur == nil ) { break; }
		if( isf == 0) { printf(" "); }
		printf( "%d", cur->key );
		cur = cur->next;
		isf = 0;
	}
	printf("\n");
}

void deleteNode( NodePointer t )
{
	NodePointer pt = t->prev;
	NodePointer nt = t->next;
	pt->next = nt;
	nt->prev = pt;
	free( t );
}

void deleteFirst( )
{
	NodePointer t = nil->next;
	if( t == nil ) return;
	deleteNode( t );
}

void deleteLast( )
{
	NodePointer t = nil->prev;
	if( t == nil ) return;
	deleteNode( t );
}

void delete( int key )
{
	NodePointer cur = nil->next;
	while( 1 ) {
		if( cur == nil ) { break; }
		if( cur->key == key ) { break; }
		cur = cur->next;
	}
	if( cur == nil ) return;
	deleteNode( cur );
}


void insert( int key )
{
	NodePointer x;
	x = malloc( sizeof(struct node) );
	x->key = key;
	x->next = nil->next;
	x->next->prev = x;
	x->prev = nil;
	nil->next = x;
}


int main( int argc, char *argv[] ) 
{
	int key, n, i;
	char com[20];
	
	scanf( "%d", &n );
	init( );
	for( i = 0; i < n; i++ ) {
		scanf( "%s", com );
		if( com[0] == 'i' ) {
			scanf( "%d", &key );
			insert( key ); 
		} else if( com[0] == 'd' ) {
			if( 6 < strlen( com )  ) {
				if( com[6] == 'F' ) { 
					deleteFirst( );
				} else if( com[6] == 'L' ) {
					deleteLast( );
				}
			} else {
				scanf( "%d", &key );
				delete( key );
			}
		}
	}
	printList( );
	
    return 0;
}