title: find missing integer
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/2946056/question-about-missing-element-in-array">question about  missing element in array</a><br>
    <a href="https://stackoverflow.com/questions/10447569/decrease-runtime-to-on">decrease runtime to O(n)</a>
    </p>
  </blockquote>
  
  <p>An array A[1   n] contains all the integers from 0 to n except for one 
  number which is missing . In this problem, we cannot access an entire 
  integer in A with a single operation . The elements of A are represented in 
  binary, and the only operation we can use to access them is “fetch the jth 
  bit of A[i]”, which takes constant time .how to do it?? Can we do it in O(n) time? </p>