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4 wheel drive
I just posted two new puzzles and as always, there is something special about at least one of them :).
The “classic” Sudoku puzzle is a 4×4, not 3×3. Use LETTERS A-P to solve it instead of digits!
The good ol’ Killer Sudoku is a little bit more difficult than yesterday’s puzzle, but surely solveable by “logic” only. I hope to implement the difficulty rating system until the end of this week and as of then you will know what kinda beast you’re dealing with.
Poll results
We’ve had more than 200 votes on the favorite Sudoku poll and I think it’s about time to close this poll, although it is likely that it will be reopened at some stage, just to re-check your opinion. Here are the results:
Gattai 5 – X
Update: The link has been fixed. Thanx to udosuk for pointing this out. You can download the Samurai now.
Here it is, another Samurai X puzzle – this is the only place you can find these kind of Sudoku puzzles! Only the visitors of this website have the privilege to download and solve such puzzles.
Basically, not only do you have to fight against 5 interconnected Sudokus, but you also need to be carefull about the diagonals: ALL diagonals in the puzzle must contain one occurrence of each 1-9 digit. The diagonals are marked in the puzzle so you wouldn’t forget about them.
Click on the puzzle thumbnail to access the puzzle.
Current progress on Sep 27
This is a response to ZD’s and udosuk’s posts and progress updates regarding solving the puzzle posted on September 27 by hand and using logic. This is how far we got – I added “9” in the last nonet as ZD suggested. From ZD’s and udosuk’s work you can also find some of the pencilmarks that can be removed from this position. Their discussion is here
If you’d like to work on this, you can open this file in any image editor (say Microsoft’s “Paint”) and delete “pencil marks” (using simple tools of your imaging software) when you figure out which values can be removed.
One suggestion – if you solve R9C1 and R1C9 the solution should unfold somewhat easier. I’m not saying this is the next logical step; I only figured that if those 2 were solved there would be no more “trial and error” needed to solve this one.
Good luck!
If you’d like to work on this, you can open this file in any image editor (say Microsoft’s “Paint”) and delete “pencil marks” (using simple tools of your imaging software) when you figure out which values can be removed.
One suggestion – if you solve R9C1 and R1C9 the solution should unfold somewhat easier. I’m not saying this is the next logical step; I only figured that if those 2 were solved there would be no more “trial and error” needed to solve this one.
Good luck!
Let’s solve this baby!
Ok, I’ve created a separate category for the Killer Sudoku puzzle posted on September 27. It’s caused a lot of controversy and discussion on other websites and it’s time to bring this baby home and solve it!
I’m really swamped with work so I haven’t had time to solve this puzzle by hand. Let’s work together until we find a “logical” step by step solution without using trial and error.
THE puzzle:
And the solution found by trial and error algorithm (and it is surely the only solution):
And the solution found by trial and error algorithm (and it is surely the only solution):
Had to post ’em :)
Well I took a day off today and didn’t think that I would post the puzzles, but once I got home I thought – why not! So, two more puzzles for your perusal over the weekend – check the daily sections.
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Cage Splitting – Killer Sudoku
Ok, here is the explanation of the “Cage/fence splitting” solving technique for Killer Sudoku puzzles that I promised before. I will use the puzzle posted on Friday, October 7 and solve it step by step using this method.
We extend the idea of the “innies” and “outies” solving technique, except that you’re not looking for one cell but for any number of them. See the explanation of innies/outies.
So, if you find, for instance, a row that has 7 cells that are in cages that completely belong to that row and the sum of all those cages is, say, 40, the remaining two cells must add up to 5, no matter in which column they are or if they’re next to one another or not.
If that sounds too complicated, let’s go back to our sample puzzle. We’re focusing on the nonet number 6. It’s made of 3 cages plus 2 cells that belong to cages outside of it. The sum of those 3 cages is 8+12+14 = 34. Therefore, the other 2 cells must add up to (rule of 45) 45-34 = 11. Do you see the point now?
Next up – nonet nr.2. We split the cage marked with 26 because we know one of it’s cells (5), so it becomes 21. Then, we look at nonets 1 and 2 and find an “innie” of those two nonets put together. It’s value is 90-(11+16+34+6+21) = 90 – 88 = 2.
The cell that we just solved (value 2) belongs to a cage marked with 11. We split that cage, so the part in the 5th nonet has the value 9. Now we look at the entire row nr.4. We see that almost all cages are completely within that row except for the cell at r5c1. So, it’s an “outie”! Rule of 45: (16+10+9+9+8) – 45 = 52 – 45 = 7. So, r5c1 = 7.
From here, there are now many paths to the correct solution. In fact it can be solved by using only Sudoku techniques (as long as you make sure your cage-sums are Ok), but there are a few more cells that can be solved using innies/outies.
The technique explained above can be quite complex depending on the puzzle. It’s quite possible that you will not be able to solve a cell by using it, but that you could remove some of the possible values for some cells. This often leads to another clue for some other cell.
Hope this was helpful.
Well, now you definitely do. One of those 2 cells belongs to a cage with sum of 3, which can only be 1+2. Since that cell must add up to 11 with another cell, 1 is simply not enough (you can’t have a 10 in the other cell). So it must be 2! Therefore, the last remaining cell in the nonet nr.6 must be 9.If anyone is still with me, the rest should be pretty straightforward. Look at nonet 3. Cage marked with 18. We found that one of it’s cells must be 9. Therefore, we split that cage and figure out that it’s 2 cells belonging to nonet 3 must add up to 18-9 = 9. So we find an “innie” in the upper left corner of nonet 3: 45-(10+9+12+9) = 45 – 40 = 5.
Next up – nonet nr.2. We split the cage marked with 26 because we know one of it’s cells (5), so it becomes 21. Then, we look at nonets 1 and 2 and find an “innie” of those two nonets put together. It’s value is 90-(11+16+34+6+21) = 90 – 88 = 2.
The cell that we just solved (value 2) belongs to a cage marked with 11. We split that cage, so the part in the 5th nonet has the value 9. Now we look at the entire row nr.4. We see that almost all cages are completely within that row except for the cell at r5c1. So, it’s an “outie”! Rule of 45: (16+10+9+9+8) – 45 = 52 – 45 = 7. So, r5c1 = 7.
From here, there are now many paths to the correct solution. In fact it can be solved by using only Sudoku techniques (as long as you make sure your cage-sums are Ok), but there are a few more cells that can be solved using innies/outies.
The technique explained above can be quite complex depending on the puzzle. It’s quite possible that you will not be able to solve a cell by using it, but that you could remove some of the possible values for some cells. This often leads to another clue for some other cell.
Hope this was helpful.
Posted in Killer Sudoku, Solving tips
Tagged Cage Splitting, innie, INNIES, innies and outies, IQ, killer, killer sudoku, outie, OUTIES, rule of 45, sample puzzle, solving technique, technique
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Two very cool puzzles today!
I’ve posted two very beautiful puzzles today.
Killer Sudoku: This one might look very difficult but after a tough first step, the solution unfolds really easy. This is at least how I got the solution :), there could be a simpler one. Anyhow, I will use this one to explain the technique that I call “fence (cage) splitting” in a couple of days.
Sudoku Variant: Well I’ve always thought that there are some similarities between Sudoku and the game of Chess. I think this puzzle proves it – isn’t it beautiful how the “pieces” are aligned? Oh yes, and it’s a diagonal sudoku, too.
Good luck and have fun.
Posted in Killer Sudoku, Solving tips
Tagged COOL, Diagonal Sudoku, EASY, IQ, killer, killer sudoku, Sudoku Variant, technique, variant
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Killer Sudoku – September 27th
Many people have asked about the Killer Sudoku posted on September 27th.
I haven’t tried to solve this Killer by hand but it is very much possible that it requires either a lot of math (the technique that I call “cage/fence splitting”, which will be explained in the next few days) or that it cannot be solved by “logic” alone, that it needs trial and error. What is certain is that it does have only one solution.
Why did I post such a puzzle? Because as you might know, the first puzzle was published on September 26. At that time, the algorithm used for producing Killer Sudokus relied heavily on “backtracking”, or trial and error in plain words.
So, one of these days I will try to solve it by “logic” (I think this term is improperly used in this context) and if I succeed I will post a step-by-step solution. If not, maybe someone will and we will be very thankful if they post their solution :).
Posted in General, Killer Sudoku, Solving tips
Tagged IQ, killer, killer sudoku, Killer Sudokus, technique
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Vote for your favourite
I added a new feature to this site – polls. Thanks to Andrew Sutherland for creating this great WordPress plugin.
The first poll is about your favourite type of Sudoku. The results will be taken into consideration when posting new puzzles, so your vote counts!
If you want me to add another option so you can vote – please send a comment to this post.
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