public static void main(String[] args) {
// 3
// 2 5
// 1 4 6
BinaryTreeNode<Integer> tree = new BinaryTreeNode<>(3);
tree.setLeft(new BinaryTreeNode<>(2));
tree.getLeft().setLeft(new BinaryTreeNode<>(1));
tree.setRight(new BinaryTreeNode<>(5));
tree.getRight().setLeft(new BinaryTreeNode<>(4));
tree.getRight().setRight(new BinaryTreeNode<>(6));
// should output true.
assert isBinaryTreeBST(tree);
System.out.println(isBinaryTreeBST(tree));
// 10
// 2 5
// 1 4 6
tree.setData(10);
// should output false.
assert !isBinaryTreeBST(tree);
System.out.println(isBinaryTreeBST(tree));
// should output true.
assert isBinaryTreeBST(null);
System.out.println(isBinaryTreeBST(null));
}
