title: Index structure for top-k queries on bitstrings
body: <p>Given array of bitstrings (all of the same length) and query string Q find top-k most similar strings to Q, where similarity between strings A and B is defined as number of 1 in A and B, (operation and is applied bitwise).  </p>
  
  <p>I think there is should be a classical result for this problem. </p>
  
  <p>k is small, in hundreds, while number of vectors in hundreds of millions and length of the vectors is 512 or 1024 </p>