Validate Binary Search Tree

Java

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: True if the binary tree is BST, or false
     */
    
    public boolean isValidBST(TreeNode root) {
        // write your code here
    
        return divConq(root, Long.MIN_VALUE, Long.MAX_VALUE);
    }
    private boolean divConq(TreeNode root, long min, long max){
        if(root == null){
            return true;
        }
        
        if(root.val <= min || root.val >= max){
            return false;
        }
        
        return divConq(root.left, min, root.val) &&
                divConq(root.right, root.val, max);
    }
}