What am I doing wrong? Surely no grid entries can be like eg 123 because the two dominoes 12 and 23 will be used with only 3 spaces so all the dominoes will be completed in less than the stated 56 spaces. And yet 6 across contains 2 dominoes!!! Help please
The dominoes do not overlap -- if there's a pattern such as 123 then, for example, the 12 forms one domino and the 3 forms part of another, possibly perpendicular. If you have the grid correctly filled there is a unique arrangement of the dominoes.