BST.java

public class BinaryTree {
    static class Node {
        //instance variable of Node class
        public int data;
        public Node left;
        public Node right;

        //constructor
        public Node(int data) {
            this.data = data;
            this.left = null;
            this.right = null;
        }
    }
    
    // instance variable of binary tree class
    public Node root;

    // constructor for initialise the root to null BYDEFAULT
    public BinaryTree() {
        this.root = null;
    }

    // method to check the given tree is Binary search tree or not
    public boolean isBSTOrNot() {
        return isBSTOrNot(this.root, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }

    private boolean isBSTOrNot(Node root, int minValue, int maxValue) {
        // check for root is not null or not
        if (root == null) {
            return true;
        }
        // check for current node value with left node value and right node value and recursively check for left sub tree and right sub tree
        if(root.data >= minValue && root.data <= maxValue && isBSTOrNot(root.left, minValue, root.data) && isBSTOrNot(root.right, root.data, maxValue)){
            return true;
        }
        return false;
    }

    
    
    public static void main(String[] args) {
        // Creating the object of BinaryTree class
        BinaryTree bt = new BinaryTree();
        bt.root= new Node(100);
        bt.root.left= new Node(90);
        bt.root.right= new Node(110);
        bt.root.left.left= new Node(80);
        bt.root.left.right= new Node(95);
        System.out.println(bt.isBSTOrNot());

    }
}