title: O(1) Delete operation
body: <p>Is there any data structure or variation of existing data structure that offers O(1) or constant time complexity for delete operation ?</p>
  
  <p>I know hash table can do it. But I am modifying hash table where, we can get all the  the keys without going through all the buckets and in order to do so I am storing every key in another linked list and at the time when I add it to hash table. So I can get all the keys in quick. </p>