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>

#define MAX 100000

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

struct Node *nil;

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

struct Node* search(int key){
	struct Node *c;
	c=nil->next;
	while(c->key!=key){
		c=c->next;
		if(c==nil){
			return (nil);
		}
	}
	return(c);
}

void insert(int key){
	struct Node* x;
	x=(struct Node *)malloc(sizeof (struct Node));

	x->key=key;
	x->next=nil->next;
	x->next->prev=x;
	nil->next=x;
	x->prev=nil;
}

void delete(struct Node * x){
	if(x==nil){
		return;
	}
	x->next->prev=x->prev;
	x->prev->next=x->next;
	free(x);
}

void deleteFirst(){
	delete(nil->next);
}

void deleteLast(){
	delete(nil->prev);
}

void printList(){
	struct Node *c;
	c=nil->next;
	while(c!=nil){
		printf("%d",c->key);
		c=c->next;
		if(c!=nil){
			printf(" ");
		}
	}
	printf("\n");
}

int main(){
	int i,n,key;
	char com[20];
	struct Node *c;

	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(strcmp(com,"deleteFirst")==0){
				deleteFirst();
			}else if(strcmp(com,"deleteLast")==0){
				deleteLast();
			}else{
				scanf("%d",&key);
				c=search(key);
				delete(c);
			}
			
		}
	}
	printList();
	
	return 0;
}