title: Given 4 billion numbers, how to find a number which is not in these 4 billion numbers? We have only 1GB of memory
body: <p>Given 4 billion numbers, how to find a number which is not in these 4 billion numbers? We have only 1GB of memory. </p>
  
  <p>The numbers can be non-consecutive.</p>
  
  <p>How to do the same in 10MB of memory?</p>