title: Minizinc search 2d array with constraints
body: <p>How could I select the smallest number from each row of a 2d array while making sure the same column can at most be selected twice
  (in the following case, for row 1, column 5 is chosen; for row 2, column 5 is chosen while for row 3, column 5 can no longer be selected, so column 2 is selected as the min):
  (Besides, in java, it is often that ArrayList is used to add and remove elements but how is it possible to do this in Minizinc using constraints)?</p>
  
  <pre><code>int: m = 3;
  int: n = 5;
  array[1..m,1..n] of int: diffs = [|14,18,24,30,13
                                    |10,12,18,24,7
                                    | 8,7,12,18,6|]
  </code></pre>