It’s not quite up there with Leonardo DiCaprio eating raw bison liver to get into character, but Michelle Yeoh reportedly spent two years learning the Rubik’s Cube to prepare for this Chinese drama in which she plays a real-life former maths teacher who became a champion in retirement. The true story is stretched and squeezed here, fictionalised to fit sports-movie formula; it ends up being so-so entertaining and funny in places, but disappointingly predictable. The biggest surprise is that cubing is so popular it has its own world championship. Still,…