So currently I’m checking the Sudoku board for 0s with only one possible solution. This works for most easy boards, but as soon as it gets medium-hard, it’s not possible to finish the board only by analyzing rows, cols and quads. I don’t know if there are any other algos for solving this in a smarter way (there 100% are), but I didn’t want to just look up a solution before I didn’t do at least a brute force method first.

• Go through all 0s
• Use their first possible number
• As soon as I hit a wall, start from beginning with the next possible number

This sounds heavy but maybe I can reduce the attempts in some way.