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 private boolean validate(TreeNode node, long min, long max) {
        if (node == null) return true;

        // Check the current node's value against the range
        if (node.val <= min || node.val >= max) return false;

        // Recursively validate the left and right subtrees
        return validate(node.left, min, node.val) && validate(node.right, node.val, max);
    }