Answer: AVL trees

Question: What single rotation can we perform on the following to make it into an AVL tree?

     4
    / \
   2   8
  /   / \
 0   7   10
          \
           11
            \
             15

Answer: Rotate the 10-11 edge to get

     4
    / \
   2   8
  /   / \
 0   7   11
        / \
       10  15