Assume that a tree is represented by X$,$ lef t$($X$),$ right$($X$)$ and possibly

other satellite data that we ignore. A tree is called an AVL tree if$,$ for every subtree

rooted at X$,$ the absolute value of the height difference between the left subtree and

the right subtree is at most $1.$ Specifically, if hL is the height of lef t$($X$)$ and hR is the

height of right$($X$),$ then $|$hL $$ hR$|1.$

Give an algorithm that checks if a tree is an AVL tree.