public boolean isValidBST(TreeNode root) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if (root == null)
			return true;
		// if (root.left == null && root.right == null) return true;

		int[] preVal = new int[1];
		preVal[0] = Integer.MIN_VALUE;
		return inOrder(root, preVal);

	}