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{
  int key;
  struct node *n,*p;
};

struct node* nil;

struct node* search(int key){
  struct node* c;
  c=nil->n;
  while(c != nil && c->key != key){
    c=c->n;
  }
  return c;
}

void init(){
  nil=(struct node *)malloc(sizeof(struct node));
  nil->n=nil;
  nil->p=nil;
}

void printlist(){
  struct node* c;
  int ss;

  c=nil->n;
  ss=0;

  while(1){
    if(c == nil)break;
    if(ss++>0)printf(" ");
    printf("%d",c->key);
    c=c->n;
  }
  printf("\n");
}

void Dnode(struct node* t){
  if(t == nil)return;
  t->p->n=t->n;
  t->n->p=t->p;
  free(t);
}
void Dfirst(){
  Dnode(nil->n);
}

void Dlast(){
  Dnode(nil->p);
}

void Dkey(int key){
  Dnode(search(key));
}

void insert(int key){
  struct node *x =(struct node *)malloc(sizeof(struct node));
  x->key=key;
  x->n=nil->n;
  nil->n->p=x;
  nil->n =x;
  x->p=nil;
}

int main(){
  int key,i,n,ss;
  ss = 0;
  char s[20];
  int n1=0,n2=0;


  scanf("%d",&n);
  init();

  for(i=0;i<n;i++){
    scanf("%s",s);
    if(s[0] == 'i'){
      scanf("%d", &key);
      insert(key);
      n1++;
      ss++;
    }
    else if(s[0] == 'd'){
      if(strlen(s) > 6){
	if(s[6] == 'F')Dfirst();
	else if(s[6] == 'L')Dlast();
      }else{
	scanf("%d", &key);
	Dkey(key);
	n2++;
      }
      ss--;
    }
  }
  printlist();

  return 0;
}