I’ve implemented Norvig for a couple languages as a learning tool. One thing I do that he didn’t before dropping to brute force though is the m squares with m

I’ve implemented Norvig for a couple languages as a learning tool. One thing I do that he didn’t before dropping to brute force though is the m squares with m possibilities check. If two squares in a row, column or group only have two possible values, then you can eliminate those possibilities from all of their siblings. Same for 3:3, 4:4 and 5:5.