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{
  struct node *prev;
  struct node *next;
  int key;
};

typedef struct node *NodePointer;
NodePointer nil;

NodePointer search(int k){
  NodePointer x;

  x=nil->next;
  while(x!=nil && x->key!=k){
    x=x->next;
  }

  return x;
}

void insert(int k){
  NodePointer x;

  x=malloc(sizeof(struct node));
  x->key=k;
  x->next=nil->next;
  nil->next->prev=x;
  nil->next=x;
  x->prev=nil;
}

void deleteNode(NodePointer x){
  x->prev->next=x->next;
  x->next->prev=x->prev;
}

void delete(int k){
  NodePointer x;

  x=search(k);
  if(x==nil) return;
  deleteNode(x);
}

void deleteFirst(){
  NodePointer x;

  x=nil->next;
  deleteNode(x);
}

void deleteLast(){
  NodePointer x;

  x=nil->prev;
  deleteNode(x);
}

int main(){
  int n,i,k,flag=1;
  char c[20];
  NodePointer x;

  nil=malloc(sizeof(struct node));
  nil->prev=nil;
  nil->next=nil;

  scanf("%d",&n);
  for(i=0;i<n;i++){
    scanf("%s",c);
    if(c[0]=='i'){
      scanf("%d",&k);
      insert(k);
    }else if(c[0]=='d'){
      if(strlen(c)>6){
	if(c[6]=='F') deleteFirst(); 
	  else if(c[6]=='L') deleteLast();
      }else{
	scanf("%d",&k);
	delete(k);
      }
    }
  }

  x=nil->next;
  while(1){
    if(x==nil) break;
    if(flag==0) printf(" ");
    printf("%d",x->key);
    x=x->next;
    flag=0;
  }
  printf("\n");

  return 0;
}