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 *next;
  struct Node *prev;
};

struct Node *nil;

struct Node* listSearch(int key)
{
  struct Node *cur=nil->next;
  while(cur!=nil&&cur->key!=key)
    {
      cur=cur->next;
    }
    
  return cur;
}

void input();
void print();
void deleteNode(struct Node *t);
void deletefirst();
void deletelast();
void deleteKey(int key);
void insert(int key);

int main(void)
{
  int i;
  int key,n;
  int size = 0;
  char com[20];
  int np=0,nd=0;
    
  scanf("%d",&n);
    
  input();
    
  for(i=0;i<n;i++)
    {
      scanf(" %s %d",com,&key);
      if(com[0]=='i')
	{
	  insert(key);
	  np++;
	  size++;
        }
      else if(com[0]=='d')
	{
	  if(strlen(com)>6)
	    {
	      if(com[6]=='F')
		{
		  deletefirst();
		}
	      else if(com[6]=='L')
		{
		  deletelast();
		}
            }
	  else
	    {
	      deleteKey(key);
	      nd++;
            }
	  size--;
        }
    }
    
  print();
    
  return 0;
    
}

void input()
{
  nil=(struct Node *)malloc(sizeof(struct Node));
  nil->next=nil;
  nil->prev=nil;
}

void print()
{
  struct Node *cur=nil->next;
    
  int i=0;
    
  while(1)
    {
      if(cur==nil)
	{
	  break;
	}
      if( i++>0 )
	{
	  putchar(' ');
	}
	
      printf("%d",cur->key);
	
      cur=cur->next;
    }
    
  putchar('\n');
}

void deleteNode(struct Node *t)
{
  if(t==nil)
    {return;
    }
    
  t->prev->next=t->next;
    
  t->next->prev=t->prev;
    
  free(t);
}

void deletefirst()
{
  deleteNode(nil->next);
}

void deletelast()
{
  deleteNode(nil->prev);
}

void deleteKey(int key)
{
  deleteNode(listSearch(key));
}

void insert(int key)
{
  struct Node *x=(struct Node *)malloc(sizeof(struct Node));

  x->key=key;   
  x->next=nil->next;
  nil->next->prev=x;
  nil->next=x;
  x->prev=nil;
}