Here's the problem and the diagram that goes with it

Fill in each empty space of the grid in the image below with a number from 1 to 8 so that every row & column contains each of these digits only once. Some diagonally adjacent spaces have been joined together. For these pairs of joined spaces the same number must be written in both. 
Diagram -> [https://imgur.com/a/sSwCPR2][1]

We had a sub the other day and he gave us this question offering extra credit to the first person who solved it. Someone already did it and got the points but we never got an explanation for the answer which I want to hear. Yes, I already asked my teacher and she said she didn't know.


  [1]: https://imgur.com/a/sSwCPR2