Saturday 1 June 2013

Daily League Sudoku #18: Factory Killer Sudoku

This week's puzzle is again harder. Especially the opening is tricky. It really helps to understand some of the implications. I don't think I've seen this variant before, but one can never be sure.
I've been planning on writing a Killer Sudoku variant for a while, but it never came of it. Either because other people had a Killer Sudoku or that my attempts failed and I eventually switched to another Sudoku type. This puzzle took me about 3 hours to get right. I could have made it easier, but I really liked the 2-4-6-8 grouping in the middle nonets, but that led to some uniqueness issues for a while. I wasn't sure if I could get the 2 nonet to work, but it eventually fell nicely. It's tricky, but I think it has a nice solution path. Enjoy.

Recap of the last Daily League week:
Sunday: FINDoku by Seungjae Kwak
Monday: Thermometer Sudoku by Fred Stalder
Tuesday: Outside-Consecutive Sudoku by Prasanna Seshadri
Wednesday: Argyle Sudoku by Bastien Vial-Jaime
Thursday: Even Queens Sudoku by Jakub Hrazdira
Friday: Number 5 Is Not Alive Sudoku by Tom Collyer

In this Sudoku there are a number of dashes cages. A number in a dashed cage indicates a factor of the sum of the digits in its cage. Digits can't repeat within a cage.


  1. I'm really impressed with how well such sparse information can lead to one solution.

    1. Thanks. I wasn't sure how to create an opening at first, but when I realised how outies could be forced I gave that a try. And when the 8 and 6 opposite eachother forced a lot I figured it was possible. But I did have to stick with smaller cages as if I were to go to more 4 cell cages, it would really become a impossible.

  2. I am sorry, but could not understand the rules. What does the "factor of the sum" means in non-mathematical language? Thanks a lot.

    1. It's a mathematical idea, but fairly simple. A "sum" is what you get when you add numbers. The "sum of the digits in the cage"... well, I assume you know what digits are, but a "cage" in this puzzle is each area with a dotted line around it.

      And a "factor" of a number is another number (sometimes the same) that can be divided into the first number without a remainder. For example, the factors of 20 are 1, 2, 4, 5, 10, and 20.

      So X is a factor of Y exactly when Y is a multiple of X. This means that for a cage numbered 4, the possible sums of the numbers in that cage are 4, 8, 12, 16, ...

    2. Thanks cyreb for explaining, I hadn't been back to check my blog this week.

    3. Thank you, cyrebjr. Yes, you´re right, I know what digits are :D

  3. I think I was most amazed by the power of "digits cannot repeat in a cage" when so few cages cross the boundaries of the 3x3 boxes!