Started with a very basic 2-D array based approach of having flags for 'X' and 'O' and taking the winner if condition matches as soon as a new value is put.(see game rules for more info) We discussed few optimisation over this, this started from here and ended on Cricket and the new rules inserted by ICC in late 2015.Basically this interview was taken by one of the directors in the company and hence proved the major bonus for me.