This is the 9th practice puzzle for the 2017 WSC.

These are the last 2 practice puzzles for the WSC. I'll be focussing on the WPC a bit for the next week. That's the championship where I'm actually competitive. I don't know whether I'll be posting puzzles yet for the WPC, but they might show up.

Nine posts also seems the appropriate number for a Sudoku competition. This time they are two practice puzzles for the instructionless round.

If someone has any specific request for a puzzle type, I might be persuaded to make another. Let me know.

I figured this is a round that might need some practice too. I don't think for either puzzle the rules are too hard to figure out. It's possible that both ideas have been done before. I can't remember seeing them before, but my memory isn't perfect. They're not exactly innovative ideas.

I think the first puzzle is probably more like a puzzle in the actual test. It's a just simple addition to a Sudoku grid. I had fun writing them, but with a bit more time I could have made them a bit nicer.

The second puzzle I'm not sure whether it qualifies as a Sudoku puzzle. It has all the rules of a normal Sudoku puzzle but it doesn't uses numbers like most Sudoku puzzles. I think the rules are pretty simple. I had a lot of fun writing them, so they should be fun to solve, I think.

Try the examples too. They're both fun puzzles too.

Rules for Sudoku

In this Sudoku the additional rules are not given. An example and solution are given of the Sudoku variant. Figure out the additional rule from the example and solve the puzzle.

Rules Puzzle #1 (highlight if needed): Each marked 2-cell area contains a 2-digit number, read left to right or top to bottom. The first marked 2-cell area seen by an arrow must contain a larger 2-digit number than the arrow.

Rules Puzzle #2 (highlight if needed): Place 8 arrows (fghimlkj) once in every row, column and marked 3x3 area. Numbers in the grid indicate how many arrows are pointing at that cell.

## Sunday, 8 October 2017

## Saturday, 7 October 2017

### WSC Practice #8: Round 13 - Puzzle 7: Joker Product Sudoku

This is the 8th practice puzzle for the 2017 WSC.

The Joker round is going to be a tricky one. I made an error in the construction of the previous Joker puzzle. Hopefully There are none in these. It's easier to make an error in these puzzles if you just fall back into your standard deductions.

This type actually appears twice in the championship as it also appears in the final team round.

The first puzzle should be a nice solve. I put in a few things that can be done with the Joker in this genre. I'm pretty sure they were easily figured out by yourself, but I think they're nice to see in a puzzle. There's still a few key deductions to find, but it should work well.

The second puzzle is much harder. It relies on a lot of clue interactions, without giving much direct information. It takes a long chain of interactions to place a few digits and consequently figure out the Joker. Even then it's not exactly easy.

I had to check a possible error. I realised I might have forgotten something, but it didn't really influence the puzzle as the deductions still held true. The dumb construction errors really don't allay my fears of making errors in this round by accidentally forgetting a Joker interaction.

Rules for Sudoku

In this Sudoku, numbers on the borders of two cells indicate the product of the digits in those 2 cells. Additionally, there is a Joker digit in the grid. This digit can take on any integer value from 1 to 9 necessary to comply with the rules. It can even take multiple different values within a single cell to satisfy different clues.

The Joker round is going to be a tricky one. I made an error in the construction of the previous Joker puzzle. Hopefully There are none in these. It's easier to make an error in these puzzles if you just fall back into your standard deductions.

This type actually appears twice in the championship as it also appears in the final team round.

The first puzzle should be a nice solve. I put in a few things that can be done with the Joker in this genre. I'm pretty sure they were easily figured out by yourself, but I think they're nice to see in a puzzle. There's still a few key deductions to find, but it should work well.

The second puzzle is much harder. It relies on a lot of clue interactions, without giving much direct information. It takes a long chain of interactions to place a few digits and consequently figure out the Joker. Even then it's not exactly easy.

I had to check a possible error. I realised I might have forgotten something, but it didn't really influence the puzzle as the deductions still held true. The dumb construction errors really don't allay my fears of making errors in this round by accidentally forgetting a Joker interaction.

Rules for Sudoku

In this Sudoku, numbers on the borders of two cells indicate the product of the digits in those 2 cells. Additionally, there is a Joker digit in the grid. This digit can take on any integer value from 1 to 9 necessary to comply with the rules. It can even take multiple different values within a single cell to satisfy different clues.

*Puzzle #1*

*Puzzle #2*

## Friday, 6 October 2017

### WSC Practice #7: Round 7 - Puzzle 3: Japanese Sums Sudoku

This is the 7th practice puzzle for the 2017 WSC.

I know this round might be a bit contentious to some people. They're afraid it's going to be too puzzly and not enough Sudoku. But just because a Sudoku is named after a puzzle genre, doesn't mean it's completely like that genre. I have a few ways I can imagine these puzzles to be far more like a Sudoku than a puzzle.

I tried to design this Sudoku to not heavily rely on being familiar with Japanese Sums as a puzzle. The logic needed isn't much different than a Killer Sudoku. This is one of the ways I imagined the Sudoku element to shine much more through than the Japanese Sums element of the puzzle. The puzzle shouldn't be too hard if you work the clues in the right order. I hope this helps prepare a bit for the championship.

Rules for Sudoku

In this Sudoku, shade some cells in the grid so that the numbers outside the grid represent the sums of the digits in the white cells in that row or column. The sums are given in the correct order. If there are multiple sums in a row or column, they need to be separated by at least one shaded cell. Some shaded cells may be given.

I know this round might be a bit contentious to some people. They're afraid it's going to be too puzzly and not enough Sudoku. But just because a Sudoku is named after a puzzle genre, doesn't mean it's completely like that genre. I have a few ways I can imagine these puzzles to be far more like a Sudoku than a puzzle.

I tried to design this Sudoku to not heavily rely on being familiar with Japanese Sums as a puzzle. The logic needed isn't much different than a Killer Sudoku. This is one of the ways I imagined the Sudoku element to shine much more through than the Japanese Sums element of the puzzle. The puzzle shouldn't be too hard if you work the clues in the right order. I hope this helps prepare a bit for the championship.

Rules for Sudoku

In this Sudoku, shade some cells in the grid so that the numbers outside the grid represent the sums of the digits in the white cells in that row or column. The sums are given in the correct order. If there are multiple sums in a row or column, they need to be separated by at least one shaded cell. Some shaded cells may be given.

### WSC Practice #6: Round 9 - Puzzle 6: Crossed Sudoku

This is the 6th practice puzzle for the 2017 WSC.

This is not a very new variant. There's been similar variants, one of them being Shaken Clones Sudoku, where digits have to be the same within certain shapes. The only thing different seems to be that the shape is set for this variant. I haven't solved many of these though, so I figured writing one would be good practice for me.

This puzzle is pretty standard. There's not really anything difficult in this puzzle. It just explores the standard things in this genre. If you want a more challenging version of this puzzle, you can remove the 2 in R5C5. The puzzle is still unique that way, but the solving process gets a bit more complicated. You can still get through it logically, but it really isn't that nice. I had made a bad deduction in construction, but it somehow hadn't affected uniqueness. I only found out in the resolve. I decided to add the 2 to just have a smooth solve again.

Rules for Sudoku

In this Sudoku, all crosses contain the exact same 5 digits in any given order. Digits may repeat along a cross.

This is not a very new variant. There's been similar variants, one of them being Shaken Clones Sudoku, where digits have to be the same within certain shapes. The only thing different seems to be that the shape is set for this variant. I haven't solved many of these though, so I figured writing one would be good practice for me.

This puzzle is pretty standard. There's not really anything difficult in this puzzle. It just explores the standard things in this genre. If you want a more challenging version of this puzzle, you can remove the 2 in R5C5. The puzzle is still unique that way, but the solving process gets a bit more complicated. You can still get through it logically, but it really isn't that nice. I had made a bad deduction in construction, but it somehow hadn't affected uniqueness. I only found out in the resolve. I decided to add the 2 to just have a smooth solve again.

Rules for Sudoku

In this Sudoku, all crosses contain the exact same 5 digits in any given order. Digits may repeat along a cross.

## Thursday, 5 October 2017

### WSC Practice #5: Round 6 - Puzzle 9: Big Small Count Sudoku

This is the Fifth practice puzzle for the 2017 WSC.

I wasn't really sure how this variant was going to work. The example has a lot of givens, so I wasn't sure how it would work from that. I set up an opening section and figured I'd go from there. The opening section actually gave more information than I expected and I managed to reduce the second half of the puzzle a bit. It wouldn't get unique though, so I added an extra circle just to fix a small uniqueness issue. It doesn't make for the prettiest Sudoku, but it's a nice result anyway.

I generally like these kind of circle count puzzles, because it gives a fun interaction. Every time a circle gets figure out, a bit of new information gets revealed. It's like you're adding extra clues to the grid during the solving process.

Rules for Sudoku

In this Sudoku there are a number of circles. A digit in a circle indicate either "the number of neighbouring digits bigger than that digit" or "the number of neighbouring digits smaller than that digit" or both. Not all possible circles are marked.

I wasn't really sure how this variant was going to work. The example has a lot of givens, so I wasn't sure how it would work from that. I set up an opening section and figured I'd go from there. The opening section actually gave more information than I expected and I managed to reduce the second half of the puzzle a bit. It wouldn't get unique though, so I added an extra circle just to fix a small uniqueness issue. It doesn't make for the prettiest Sudoku, but it's a nice result anyway.

I generally like these kind of circle count puzzles, because it gives a fun interaction. Every time a circle gets figure out, a bit of new information gets revealed. It's like you're adding extra clues to the grid during the solving process.

Rules for Sudoku

In this Sudoku there are a number of circles. A digit in a circle indicate either "the number of neighbouring digits bigger than that digit" or "the number of neighbouring digits smaller than that digit" or both. Not all possible circles are marked.

### WSC Practice #4: Round 13 - Puzzle 9: Joker Battenburg Sudoku

The fourth practice puzzle for the 2017 WSC.

I feel this round can use all the practice necessary. The Joker rule is something new, as far as I'm aware, and seems to be a bit tricky. Basically the Joker only follows the standard Sudoku rules, but ignores any variant in the puzzle. This is because the Joker digit can assume whatever digit it needs to be for the puzzle to work, even if it means being different digits in the same cell.

The Battenburg Sudoku was one of my own inventions. The reason I picked this type first is because it has both a positive and a negative rule in effect as all possible markings are given. The "All possible markings" rule is a bit odd with the Joker. The way I understand it, in the given solution there are no places where any extra markings HAVE TO be placed. Even if there are markings that could be placed if the Joker assumes the correct parity, they don't have to be placed as the Joker can assume an incorrect parity. I do hope my interpretation is correct, but it seems to conform with the given example in the Instruction Booklet. If it isn't, my apologies for providing an incorrect puzzle. It has happened before. It should still be fun to solve.

I think the puzzle worked out pretty well. The opening should properly show the way this variant interacts with the Joker. Once you've determined the value of the Joker, the solve really takes off. It's probably a harder puzzle because you have to keep reminding yourself of the Joker rule and thread carefully through the puzzle.

[Edit: Puzzle image fixed.]

Rules for Sudoku

In this Sudoku, everywhere a 2x2 square forms a Checkerboard pattern of Odd and Even digits a Battenburg marking is given. All possible Battenburg markings have been given.

Additionally, one digit in the puzzle is a Joker. This Joker digit can be both Odd or Even. The same Joker cell may assume different parities for different 2x2 areas.

I feel this round can use all the practice necessary. The Joker rule is something new, as far as I'm aware, and seems to be a bit tricky. Basically the Joker only follows the standard Sudoku rules, but ignores any variant in the puzzle. This is because the Joker digit can assume whatever digit it needs to be for the puzzle to work, even if it means being different digits in the same cell.

The Battenburg Sudoku was one of my own inventions. The reason I picked this type first is because it has both a positive and a negative rule in effect as all possible markings are given. The "All possible markings" rule is a bit odd with the Joker. The way I understand it, in the given solution there are no places where any extra markings HAVE TO be placed. Even if there are markings that could be placed if the Joker assumes the correct parity, they don't have to be placed as the Joker can assume an incorrect parity. I do hope my interpretation is correct, but it seems to conform with the given example in the Instruction Booklet. If it isn't, my apologies for providing an incorrect puzzle. It has happened before. It should still be fun to solve.

I think the puzzle worked out pretty well. The opening should properly show the way this variant interacts with the Joker. Once you've determined the value of the Joker, the solve really takes off. It's probably a harder puzzle because you have to keep reminding yourself of the Joker rule and thread carefully through the puzzle.

[Edit: Puzzle image fixed.]

Rules for Sudoku

In this Sudoku, everywhere a 2x2 square forms a Checkerboard pattern of Odd and Even digits a Battenburg marking is given. All possible Battenburg markings have been given.

Additionally, one digit in the puzzle is a Joker. This Joker digit can be both Odd or Even. The same Joker cell may assume different parities for different 2x2 areas.

## Wednesday, 4 October 2017

### WSC Practice #3: Round 6 - Puzzle 1: Incremental Arrow Sudoku

This is the third practice puzzle for the 2017 WSC.

Obviously some of the puzzles are going to come from the 6th round as it has new types. I figured I might as well start at the beginning of the round. This also seemed like a type that would suit my writing style.

The overall design idea was to make a long arrow and match the givens in the same place. I think it worked out well. The other 2 matching arrows just add a little bit extra to the aesthetics. This is probably the easiest puzzle out of the three practice puzzles so far. It's really a matter of making one single opening deduction and the rest of the puzzle flows pretty easily.

Rules for Sudoku

In this Sudoku, there are a number of arrows. Starting from the third digit on the arrow, each digit is the unit's digit of the sum of the previous two digits on the arrow.

Obviously some of the puzzles are going to come from the 6th round as it has new types. I figured I might as well start at the beginning of the round. This also seemed like a type that would suit my writing style.

The overall design idea was to make a long arrow and match the givens in the same place. I think it worked out well. The other 2 matching arrows just add a little bit extra to the aesthetics. This is probably the easiest puzzle out of the three practice puzzles so far. It's really a matter of making one single opening deduction and the rest of the puzzle flows pretty easily.

Rules for Sudoku

In this Sudoku, there are a number of arrows. Starting from the third digit on the arrow, each digit is the unit's digit of the sum of the previous two digits on the arrow.

### WSC Practice #2: Round 1 - Puzzle 5: 12 Sum/Product Sudoku

The second practice puzzle for the 2017 WSC.

This second puzzle is a type I don't necessarily remember solving before, but it's not exactly a new type. There's been numerous similar variants with products and sums, but this one only uses the number 12. It is the 12th WSC, so it isn't that surprising a twist.

It's impossible to write a puzzle without any given digits, as there is no way to differentiate between a number of digits. So I decided to find a nice layout of givens and work with that. The centred 1-9 is always a nice layout to choose and it actually led to some nice interactions with the 12-dots. So I designed the rest of the dots around that to make the puzzle unique. I think it worked out well. I can't really judge the difficulty, although it might be trickier than it felt designing as one deduction came about by accident as I missed it was forced pretty much from the start and went with it. Hope it's useful and fun to solve.

Rules for Sudoku

In this Sudoku there are a number of grey dots between cells. If there's a grey dot between two cells, the sum or product of the two digits in these cells must be 12. Not all possible dots have been marked.

This second puzzle is a type I don't necessarily remember solving before, but it's not exactly a new type. There's been numerous similar variants with products and sums, but this one only uses the number 12. It is the 12th WSC, so it isn't that surprising a twist.

It's impossible to write a puzzle without any given digits, as there is no way to differentiate between a number of digits. So I decided to find a nice layout of givens and work with that. The centred 1-9 is always a nice layout to choose and it actually led to some nice interactions with the 12-dots. So I designed the rest of the dots around that to make the puzzle unique. I think it worked out well. I can't really judge the difficulty, although it might be trickier than it felt designing as one deduction came about by accident as I missed it was forced pretty much from the start and went with it. Hope it's useful and fun to solve.

Rules for Sudoku

In this Sudoku there are a number of grey dots between cells. If there's a grey dot between two cells, the sum or product of the two digits in these cells must be 12. Not all possible dots have been marked.

## Tuesday, 3 October 2017

### WSC Practice #1: Round 2 - Puzzle 22: Outside 234 Sudoku

This is the first proper practice puzzle for the 2017 WSC.

I've written this type a couple of times, usually under the name Inside Sudoku. One of them was used at the 2016 Thai Open and another one can be found on my blog. The logic is pretty similar to Outside Sudoku, but the small twist makes it different enough to qualify as a different variant. Because it's a newer variant, I enjoy writing these a bit more.

This puzzle has a type of opening that works nicely in this variant. I think you need to fully understand the implications of the opening to get your way through the puzzle. It's not the easiest opening, but should be useful to understand the full implications of this variant. The solve around it shouldn't be overly hard. I sacrificed symmetry a bit to keep a nicer solve. I always prefer nice logic over nice aesthetics, although both together is obviously better.

Rules for Sudoku

In this Sudoku, clues are given on the outside. Digits on the outside indicate that these digits appear in the 2nd, 3rd or 4th cell in that row or column when looking from that side.

I've written this type a couple of times, usually under the name Inside Sudoku. One of them was used at the 2016 Thai Open and another one can be found on my blog. The logic is pretty similar to Outside Sudoku, but the small twist makes it different enough to qualify as a different variant. Because it's a newer variant, I enjoy writing these a bit more.

This puzzle has a type of opening that works nicely in this variant. I think you need to fully understand the implications of the opening to get your way through the puzzle. It's not the easiest opening, but should be useful to understand the full implications of this variant. The solve around it shouldn't be overly hard. I sacrificed symmetry a bit to keep a nicer solve. I always prefer nice logic over nice aesthetics, although both together is obviously better.

Rules for Sudoku

In this Sudoku, clues are given on the outside. Digits on the outside indicate that these digits appear in the 2nd, 3rd or 4th cell in that row or column when looking from that side.

## Monday, 2 October 2017

### Daily League Sudoku #69: Palindrome Sudoku

I've been intending to post some puzzles on my blog, but that never really seems to happen. I wrote a couple of Sudokus for the Daily League to post in the upcoming weeks. But as the Instruction Booklet of the WSC just came out, I've noticed some of the variants I wrote are useful as practice for the WSC. So I'll be uploading those puzzles earlier than planned. I will try to post a Sudoku and/or puzzle a day as practice for the WSC, but I could be missing a puzzle once in a while.

This first puzzle does not actually appear as a separate variant in the WSC, but the practice might be useful. I enjoyed the opening of this puzzle. The original design had a symmetric layout, but the extra clues somewhat invalidated the created opening, so I reduced the puzzle a bit to make the solve come through more. This is the third Palindrom Sudoku I've written and for some reason the centre of the sequence seems to always end up between R2C3 and R1C4. Clearly this seems like the right point to start a line for me.

Rules for Sudoku

In this Sudoku, the digits along the grey line form a palindromic sequence. This means the digits along the line read the same starting from either end.

This first puzzle does not actually appear as a separate variant in the WSC, but the practice might be useful. I enjoyed the opening of this puzzle. The original design had a symmetric layout, but the extra clues somewhat invalidated the created opening, so I reduced the puzzle a bit to make the solve come through more. This is the third Palindrom Sudoku I've written and for some reason the centre of the sequence seems to always end up between R2C3 and R1C4. Clearly this seems like the right point to start a line for me.

Rules for Sudoku

In this Sudoku, the digits along the grey line form a palindromic sequence. This means the digits along the line read the same starting from either end.

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