title: How to find a set of values from a list of lists which contains no repetitions
body: <p>You have a list of lists in Python, something like this:</p>
  
  <pre><code>l = [[ 1,  2,  3],
       [18, 20, 22],
       [ 3, 14, 16],
       [ 1,  3, 05],
       [18,  2, 16]]
  </code></pre>
  
  <p>How would you go about selecting one value from each sub-list, such that no single value is repeated, and the sum of the resulting list is minimised?</p>
  
  <pre><code>result = [1, 18, 3, 5, 2]
  </code></pre>