public class Solution {

    List<Integer> list = new ArrayList<>();

    public boolean isValidBST(TreeNode root) {

        if(root == null)

        {

            return true;

        }

        inorderTraversal(root);

        for(int i = 0; i < list.size() - 1; i ++)

        {

            if(list.get(i) >= list.get(i+1))

            {

                return false;

            }

        }

        return true;

    }

    public void inorderTraversal(TreeNode root)

    {

        if(root == null)

        {

            return ;

        }

        inorderTraversal(root.left);

        list.add(root.val);

        inorderTraversal(root.right);

    }

}

public boolean isValidBST3(TreeNode root) {

	        return isValidBST(root, null, null);

	    }

	    public boolean isValidBST(TreeNode root, Integer min, Integer max)

	    {

	        if(root == null)

	        {

	            return true;

	        }

	        if(min != null && root.val <= min)

	        {

	            return false;

	        }

	        if(max != null && root.val >= max)

	        {

	            return false;

	        }

	        return isValidBST(root.left, min, root.val) && isValidBST(root.right, root.val, max);

	    }