Some time ago a friend told me about a solver for polycube puzzles he had written in Haskell. When I asked if I could see the code he wasn't able to find the complete code but could dig up some blog posts in which he described the algorithm (look for "Applied Cubism") and posted some parts of the code.
He also "challenged" me to fill in the blanks and thus recreate his complete algorithm.
Which I did not do. Instead I took his description of the backtracking algorithm and some ideas for the appropriate types and rewrote the algorithm from scratch. Along the way I also added a solver for polyomino puzzles puzzles as well.