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>

#define N 2000000

void init();
void insert(int);
struct link * search(int);
void delete(struct link *);
void print();

struct link{
	int key;
	struct link *back,*next;
};

struct link *nil;

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

void insert(int key){
	struct link *node = (struct link *) malloc(sizeof(struct link));
	node->key = key;

	node->next = nil->next;
	nil->next->back = node;
	nil->next= node;
	node->back = nil;
}

struct link * search(int key){
	struct link *t = nil->next;
	while(t->key != key || t != nil)
		{t = t->next;}
	return t;
}

void delete(struct link *x){
	printf("7");
	if(x==nil) return;
	x->back->next = x->next;
	x->next->back = x->back;
	free(x);
}

void print(){
	struct link *x;
	x = nil->next;
	while(1){
		if(x == nil){
			break;
		}
		printf("%d ",x->key);
		x = x->next;
	}
	printf("\n");
}

int main(){
	int key;
	int n,i;
	char ins[20];
	scanf("%d",&n);
	init();
	for(i=0;i<n;i++){
		scanf("%s%d",ins,&key);
		if(!strcmp(ins,"insert")){
			insert(key);
		}
		else if(ins[0]== 'd'){
			if(strlen(ins) > 6){
				if(ins[6] == 'F'){
					delete(nil->next);
				}
				else if(ins[6] == 'L'){
					delete(nil->back);
				}
			}
			else{
				delete(search(key));
			}
		}

	}
	print();
	return 0;
}