title: C# remove duplicates from List<List<int>>
body: <p>I'm having trouble coming up with the most efficient algorithm to remove duplicates from <code>List&lt;List&lt;int&gt;&gt;</code>, for example (I know this looks like a list of <code>int[]</code>, but just doing it that way for visual purposes:</p>
  
  <pre><code>my_list[0]= {1, 2, 3};
  my_list[1]= {1, 2, 3};
  my_list[2]= {9, 10, 11};
  my_list[3]= {1, 2, 3};
  </code></pre>
  
  <p>So the output would just be</p>
  
  <pre><code>new_list[0]= {1, 2, 3};
  new_list[1]= {9, 10, 11};
  </code></pre>
  
  <p>Let me know if you have any ideas. I would really appreciate it.</p>