Rotation

Now that we can add users to our new Red Black Tree, we need to add the rotation functionality that will keep it balanced and running fast!

1. Complete the rotate_left method. It takes a single node, pivot_parent, as input and rotates the tree with its pivot node – which in this case is its right child.
   1. If pivot_parent is nil or pivot_parent's right child is nil, return. Nothing to do here.
   2. Let pivot be pivot_parent's right child.
   3. Set pivot_parent's right child to be pivot's left child.
   4. If pivot's left child isn't a nil leaf node, set pivot's left child's parent to pivot_parent.
   5. Set pivot's parent to pivot_parent's parent.
   6. If pivot_parent is the root, set the root to pivot.
      1. Otherwise, if pivot_parent is its parent's left child, set pivot_parent's parent's left child to pivot.
      2. Otherwise, if pivot_parent is its parent's right child, set pivot_parent's parent's right child to pivot.
   7. Set pivot's left child to be pivot_parent.
   8. Set pivot_parent's parent to be pivot.
2. Complete the rotate_right method with all the directionality inverted.