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<string.h>
#include<stdlib.h>


typedef struct dlobj{
  int key;
  struct dlobj *next;
  struct dlobj *prev;
}dlobj;


typedef struct dlist{
  dlobj *head;
  dlobj *tail;
  int size;
}dlist;


dlist *mk_dlist(){
  dlist *p;
  p=malloc(sizeof(dlist));
  p->head=NULL;
  p->tail=NULL;
  p->size=0;
  return p;
}


void insert(dlist *L,int x){
  dlobj *p;
  p=malloc(sizeof(dlobj));
  p->key=x;
  p->next=L->head;
  if(L->head!=NULL) L->head->prev=p;
  else L->tail=p;
  L->head=p;
  p->prev=NULL;
}

void delete(dlist *L,int x){
  dlobj *p;
  p=L->head;
  while(p!=NULL){
    if(p->key==x){
      if(p->next!=NULL) p->next->prev=p->prev;
      else L->tail=p->prev;
      if(p->prev!=NULL) p->prev->next=p->next;
      else L->head=p->next;
      break;
    }
    p=p->next;
  }
}

void delete_f(dlist *L){
  if(L->head!=NULL){
    if(L->head->next==NULL) L->tail=NULL;
    L->head=L->head->next;
    if(L->head!=NULL) L->head->prev=NULL;
  }
}

void delete_l(dlist *L){
  if(L->tail!=NULL){
    if(L->tail->prev==NULL) L->head=NULL;
    L->tail=L->tail->prev;
    if(L->tail!=NULL) L->tail->next=NULL;
  }
}



int main(){
  int i;
  int n;
  char c[13];
  int x;
  dlist *L;
  L=mk_dlist();
  
  
  scanf("%d",&n);
  for(i=0;i<n;i++){
    scanf("%*[\n]%s",c);
    if(c[0]=='i'){
      scanf("%*[^1-9]%d",&x);
      insert(L,x);
    }
    else if(c[6]=='F') delete_f(L);
    else if(c[6]=='L') delete_l(L);
    else{
      scanf("%*[^1-9]%d",&x);
      delete(L,x);
    }
  }
  

  dlobj *p;
  p=L->head;
  if(p!=NULL){
    printf("%d",p->key);
    p=p->next;
  }
  while(p!=NULL){
    printf(" %d",p->key);
    p=p->next;
  }
  printf("\n");
  return 0;
}