public boolean isBST(BinaryTreeNode<Integer> root) {
if (root == null) return true;
boolean leftValid = root.getLeft() == null ? true : max(root.getLeft()) <= root.getValue();
boolean rightValid = root.getRight() == null ? true : max(root.getRight()) > root.getValue();
if (leftValid && rightValid) {
return isBST(root.getLeft()) && isBST(root.getRight());
}
return false;
}
public static void main(String[] args) {
BinaryTreeNode<Integer> root = new BinaryTreeNode<Integer>(3);
BinaryTreeNode<Integer> node1 = new BinaryTreeNode<Integer>(1);
BinaryTreeNode<Integer> node2 = new BinaryTreeNode<Integer>(5);
BinaryTreeNode<Integer> node3 = new BinaryTreeNode<Integer>(0);
BinaryTreeNode<Integer> node4 = new BinaryTreeNode<Integer>(2);
BinaryTreeNode<Integer> node5 = new BinaryTreeNode<Integer>(-1);
BinaryTreeNode<Integer> node6 = new BinaryTreeNode<Integer>(4);
root.setLeft(node1);
root.setRight(node2);
node1.setLeft(node3);
node1.setRight(node4);
node3.setLeft(node5);
node2.setLeft(node6);
BinaryTreeBST bst = new BinaryTreeBST();
System.out.println(bst.isBST(root));
}
public Integer max(BinaryTreeNode<Integer> node) {
while (node.getRight() != null) {
node = node.getRight();
}
return node.getValue();
}