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>

struct Node{
  int key;
  struct Node *next, *prev;
};
struct Node *n;
struct Node* LS(int key){
  struct Node *c=n->next;
  while(c!=n && c->key!=key){
    c=c->next;
  }
  return c;
}

void printList(void);
void ins(void);
void dele(struct Node *);
void dF(void);
void dL(void);
void deke(int);
void inke(int);

int main(){
  int key,n,i,np=0,nd=0;
  int size=0;
  char comm[20];
  scanf("%d",&n);
  ins();
  for(i=0;i<n;i++){
    scanf("%s%d",comm,&key);
    if(comm[0]=='i'){
      inke(key);
      np++;
      size++;
    }
    else if(comm[0]=='d'){
      if(strlen(comm)>6){
	if(comm[6]=='F')dF();
	else if(comm[6]=='L')dL();
      }
      else{
	deke(key);
	nd++;
      }
      size--;
    }
  }
  printList();
  return 0;
}
void printList(void){
  struct Node *c=n->next;
  int is=0;
  while(1){
    if(c==n)break;
    if(is++>0)printf(" ");
    printf("%d",c->key);
    c=c->next;
  }
  printf("\n");
}
void ins(void){
  n=(struct Node *)malloc(sizeof(struct Node));
  n->next=n;
  n->prev=n;
}
void dele(struct Node *ti){
  if(ti==n)return;
  ti->prev->next=ti->next;
  ti->next->prev=ti->prev;
  free(ti);
}
void dF(void){
  dele(n->next);
}
void dL(void){
  dele(n->prev);
}
void deke(int key){
  dele(LS(key));
}
void inke(int key){
  struct Node *x=(struct Node *)malloc(sizeof(struct Node));
  x->key=key;
  x->next=n->next;
  n->next->prev=x;
  n->next=x;
  x->prev=n;
}