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>

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

Node *nil;

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

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

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

void deleteNode(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));
}

int main(){
	int i,j=0,num,key;
	char order[15];
	Node *cur;
	
	scanf("%d",&num);
	init();
	for(i=0; i<num; i++){
		scanf("%s%d",order,&key);
		if(order[0]=='i') insert(key);
		else if(order[0]=='d'){
		if(order[6]=='F') deleteFirst();
		else if(order[6]=='L') deleteLast();
		else deleteKey(key);
		}
	}
	cur  = nil->next;
	while(1){
		if(cur == nil) break;
		if(j++ > 0) printf(" ");
		printf("%d",cur->key);
		cur = cur->next;
	}
	printf("\n");
		
	return 0;
}