I've received a lot of interesting comments and questions from Sudoku fans over the last few years and this page
is where I try to answer them. Please feel free to drop me a note on the side of the page or try the Facebook
comment box. Or you can email me directly at andrew@str8ts.com.
Post a Comment or Question here...
... by: Amy Hartner, U.S.A.
Thank you so much! A very evil sudoku plagued me for days until I came to this site and learned the X Wing Strategy. I look forward to using it in the future. I feel like a pro.
Andrew Stuart writes (16-May-2013):
Very glad the website is working for you, have fun!
... by: PeteTy, usa
28apr2013 killer
was rather hard took me about 45 min by P&P
killer solver
order of operations
row 1+2
5(2) cage with outie 4 next step...
Solver comment:
Killer Hard Combinations
KILLER COMBO (Hard) on B7: cage of size 2 with clue of 5+ can only be 1/2/4/7/9, removing 3/5/6/8
just kind of wondering what easy combinations are
5(2) cage cant have 56789 which is probably a human ez step
a 2 cage with a 4 in one cell seems sort of obvious to me
also i was unchecking all the normal sudoku boxes i could
and noticed the check box for diabolical and extreme
preforms an xor with all the checked boxes
I assumed it would turn them all on or off
Andrew Stuart writes (30-Apr-2013):
I split the combinations strategy into two parts because one is much easier than another - in most cases. The 'easy' is where a cage has only one combination. From that it will be fairly obvious what candidates can be pruned. The 'hard' is where several combinations are possible and its more work to work out what can be removed just from the combinations. The solver does take into account what remains so easy and hard are not fixed. However, if you are half way through a puzzle lots of other eliminations may make a so-called hard relatively easy to work out, combination wise. I was thinking in terms of how a human would approach a puzzle and they, I assume, would want to pick off the easy combination cages first.
The XOR on the groups of strategies is by design but I can't remember why I did it like that : )
... by: Dale E. Kloss, Portland, Oregon, USA
I was working a Jigsaw Sudoku and it occurred to me to ask:
For a Jigsaw puzzle maker, how many unique puzzle shapes could be made?
Note that I'm asking about ONLY puzzle SHAPES not where each number goes.
Thanks. Dale Kloss
Andrew Stuart writes (30-Apr-2013):
I do not know, to be honest. That’s a difficult combinatorics problem. For a jigsaw shape pattern to be 'nice' I prefer never to use cages that approximate a row or column, ie more than 7 cells in a line. That removes a large number. To still be Sudoku the shapes shouldn't map onto existing constraints. Reflection, rotation and other symmetries multiply the total number of 'unique' patterns.
... by: masonx, usa
This is great , I love to do these puzzles in the newspaper. I don't always have enough time before work and could use just a hint or two without screwing up the whole puzzle. If I have time I will do it alone. Thanks for sharing this , it works great.
... by: John, USA
What is the "solve path"?
Andrew Stuart writes (15-Apr-2013):
The series of strategies used to solve the puzzle. From the solver these are "minimally required" meaning that they are the simplest strategies at each step that gets some result. I cannot say that the solver solve path is perfectly optimal since it's down to my choice of the order in which strategies are tested, and in the advanced ones, its difficult to say which are more complex, but a computer is linear, so I have to give it an order in which to search. A truly optimal "solve path" would branch through all strategies and work out the least number of operations to solve as well as taking into account the complexity of each choice, but I can't present that on the website at this stage (too complex, too much CPU) but it’s something I'd like to develop further.
... by: Geoff, England
Sorry Andrew, still getting the 'wait' state on naked quads There is a Killer Sudoku board I would like you to look at Click on this linkAndrew Stuart writes (5-Apr-2013):
Your example puzzle helped me find another string with not enough space. Fixed and your puzzle runs through now.
Thanks for writing in and letting me know!
... by: Roman, Australia
Solver 1.91 is hanging up and giving message: Scripts out of date - clear your cache
Andrew Stuart writes (23-Mar-2013):
Hi All
I just figured it out this morning. I’d accidentally deleted a couple of lines of code in the last update – to do with the step-by-step solve part. Odd thing is they are so critical I don’t see how it worked when I tested it. Or how it sometimes works and sometimes don’t. Have a go now.
... by: ejshan, usa
the grader doesn't seem to be working any longer. use the site almost every day
Andrew Stuart writes (22-Mar-2013):
Are you seeing version 1.91 (the latest) or 1.90 ? I updated all the solvers yesterday and any cached pages will not in all likelyhood work
... by: Rich Rice, USA
having problems with naked quads says "wait" forever
Andrew Stuart writes (22-Mar-2013):
That "wait" message means the back end is not returning a result. I updated the solvers yesterday and I suspect it’s a caching issue. Are you seeing version 1.91 (the latest) or 1.90? Windows or Mac?
... by: Xavier, France
Dear, I remark that the sum of the numbers inside an area is not checked. For example, here is [ LINK] a killersudoku that is correct with respect to the sudoku rules but not with respect to the killer rules. The area starting in C3 should sum up to 17 but the solver propose a sum of 20 and seems to be happy with it. Yours. Xavier. Andrew Stuart writes (26-Feb-2013):
This is an interesting issue. Partly the solver and the user interface assumes that if all your numbers add up to 405 then you haven't made a mistake in individual cages (at least two). The solver doesn't know if you have made a mistake until the end - when it has the solved cells. And if the puzzle finishes without an error, does it need to check? In this case it does. Are you certain the original puzzle has 17 in that cage? One other cage must also be wrong. I'm too lazy to add up all the numbers from a screen shot, but if you use the "Email this Board" button I can check. Usually these sorts of problems are due to the puzzle maker not being aware/or using the Killer Cage Convention which this solver adheres to. I cant see an example in this solution, so that probably not the answer
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