title: Given a 2D array of numbers, find clusters
body: <p>Given a 2D array, for example:</p>
  
  <pre><code>0 0 0 0 0
  0 2 3 0 1
  0 8 5 0 7
  7 0 0 0 4
  </code></pre>
  
  <p>Output should be groups of clusters:</p>
  
  <p>Cluster 1: <code>&lt;2,3,8,5,7&gt;</code></p>
  
  <p>Cluster 2: <code>&lt;1,7,4&gt;</code></p>