title: Quickest way to find missing number in an array of numbers
body: <p>I have an array of numbers from 1 to 100 (both inclusive). The size of the array is 100. The numbers are randomly added to the array, but there is one random empty slot in the array. 
  What is the quickest way to find that slot as well as the number that should be put in the slot? A Java solution is preferable.</p>