I completed the beginner solution yesterday; here is the intermediate one today. Fun challenge. The basic idea is to add 45 on all rows and columns; this would ensure that the numbers 1-9 are only being used once per box.
First generate the possible solutions by row or record ID; then find the unique number not already used on other solutions and plug it in.
By the way, I was blown away with the macros and R snippets solving the advanced one; I always enjoy looking at your workflows.