int avh1(Tree t) {
  if ( t.left == null && t.right == null ) {
    return 0;
  }
  else {
    return (  t.left.leafCount*(avh1(t.left) + 1)
            + t.right.leafCount*(avh1(t.right) + 1))
          /  (t.left.leafCount() + t.right.leafCount())
  }
}