title: How to check duplicate values horizontally and vertically in a 2D array?
body: <p>Let's say I have an array like this : </p>
  
  <pre><code>9 1 2 0 
  1 5 2 5 
  7 1 6 3 
  4 3 2 7 
  </code></pre>
  
  <p>I want to be able to create a loop that goes through the array vertically and horizontally to see if there's any duplicates.<br>
  For example, it will first check 9 1 7 4 to see if there's a dups. Then 1 5 1 3 and so on.<br>
  After that, it'll do 9 1 2 0  (which will tell me there's a dup), then 1 5 2 5 7, etc etc.<br>
  How can I do that?</p>