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>
#define M 100000
typedef struct node *link;
struct node{long int v; link next; link back;};
link NEW(long int v){
	link x = malloc(sizeof(*x));
	x->v = v;
	return x;
}

void traverse(link head,link end){

	link t;
	t = head->next;

	while(t != end){
		if(t->next==end) printf("%ld",t->v);
		else printf("%ld ",t->v);
		t = t->next;
	}

	printf("\n");

	return;

}

void delete_x(link x){

	x->back->next = x->next;
	x->next->back = x->back;

	return;
}

void insert(link x, link ins){

	ins->next = x->next;
	ins->back = x;
	x->next->back = ins;
	x->next = ins;

	return;
}

link search(link head, link end, long int v){
	link t =head->next;
	while(t != end){
		if(t->v==v){
			return t;
		}
		t = t->next;
	}

	return end;
}

int main(void){

	link head,end,t,a[M];
	head = NEW(-1);
	end = NEW(-1);
	head->next=end;
	end->back=head;

	char com[11];
	int i,j,n;
	long int v;
	scanf("%d",&n);


	for(i=0;i<n;i++){

		scanf("%s",com);
	
	if(strcmp(com,"insert")==0){	
	scanf("%ld",&v);
	a[j] = NEW(v);
	insert(head,a[j]);
	j++;
	}
	
	if(strcmp(com,"delete")==0){
	scanf("%ld",&v);
	t = search(head,end,v);
	if(t!=end) delete_x(t);
	}

	if(strcmp(com,"deleteFirst")==0){
	delete_x(head->next);
	}
	if(strcmp(com,"deleteLast")==0){
	delete_x(end->back);
	}

	}

	traverse(head,end);

	return 0;
}