title: Storing postorder sequence in array
body: <p>In the code below, the nodes of a postorder tree traversal is always printed
  I m wondering if there is a way to store these nodes in the postorder sequence in an array
  Do i have to do the traversal in a iterative way?</p>
  
  <pre><code>public static void postOrder(TreeNode root) {
    if (root != null) {
      postOrder(root.left);
      postOrder(root.right);
      System.out.print(root.item + "  ");
    } else {
      return;
    }
  }
  </code></pre>