CODE EXAMPLE FOR CSHARP

uni valued tree

    public static int CountUnivalSubtrees(Node node) 
    {
        if (node == null)
            return 0;

        int count = CountUnivalSubtrees(node.left);
        count += CountUnivalSubtrees(node.right);

        return IsUnivalTree(node) ? count + 1 : count;
    }

    private static bool IsUnivalTree(Node node) 
    {
        if (node == null)
            return true;
        if (node.left != null && node.left.val != node.val)
            return false;
        if (node.right != null && node.right.val != node.val)
            return false;
        return IsUnivalTree(node.left) && IsUnivalTree(node.right);
    }