title: Why is element zero of a heap array not used?
body: <p>Here's my rough sketch of the beginning of a heap with arbitrary values</p>
  
  <pre><code> 0   1    2    3    4    5    6    7    8    9   ...
  [-] [10] [14] [15] [22] [21] [24] [23] [44] [30] ...
  </code></pre>
  
  <p>Why must the element in array[0] always be set to null?<br>
  Or why is it that we are not supposed to use it?</p>