title: Remove elements from one NSMutableArray which are contained in another array
body: <p>I have two arrays, A and B. </p>
  
  <p>How can I remove elements from A, if those elements exist in B?</p>
  
  <p>e.g. Array A:{1,2,3,4,5}, array B:{1,3}</p>
  
  <p>I would like to remove 1 and 3 from array A such that array A only contains 2,4,5 after the operation.</p>
  
  <p>Besides looping, is there any more efficient approach to doing it?</p>