title: Reverse List<List<Integer>> using Collection
body: <p>How do I reverse a List of List using Collection?</p>
  <p>Example: <code>[ [5], [10,15], [20,2] ]</code> to be <code>[ [20,2], [10,15], [5] ]</code></p>
  <p>So I have:</p>
  <pre><code>public List&lt;List&lt;Integer&gt;&gt; levelOrderBottom(TreeNode root){
     List&lt;List&lt;Integer&gt;&gt; result = new ArrayList&lt;List&lt;Integer&gt;&gt;();
     Queue&lt;TreeNode&gt; Q = new LinkedList&lt;&gt;();
     ... add stuff in Q
     result.add(nodes);
     return Collections.reverse(result); // what I want to do but its ArrayList&lt;List&gt; not ArrayList
  }
  </code></pre>
  <p>I know I can do <code>result.add(0, nodes)</code> to add it to the front of the ArrayList, but I would like to solve this issue using Collection</p>
  <p>Thank you</p>
  <p>This is my error:</p>
  <pre><code>Line 36: error: incompatible types: void cannot be converted to List&lt;List&lt;Integer&gt;&gt;
      return Collections.reverse(result);
  </code></pre>