nr. 940 - Daily League Sudoku - Even Group-Inequility Sudoku

I like the sudokus where you have to mark the odd-even cells. Such as Mathrax or yesterday Odd-Even Count Sudoku by Prasanna Seshadri.
Here is another this kind of sudoku.

Rules for Even Group-Inequility Sudoku:

Follow Sudoku rules. The given inequalities show that which side contain more even digits. Such as the first sign in the second row show that the first 3 cells contain more even digits then the second 3 cells.

nr. 941 - Daily League Sudoku - Sudoku Curve

This is my 100th post on this blog. Let's celebrate it with a sudoku. :P
Here is an easy practise puzzle for the upcoming WSC.

Rules for Sudoku Curve:
Follow Sudoku rules. The digits 1-9 appear once i each of the five 3x3 boxes and 10 bent "rows" (indicated by light curved lines). All "rows" contain exactly 9 cells.

nr. 942 - Daily League Sudoku - Rossini Sudoku

Today sudoku is an inequility variant which appeared on an LMI test in 2011 then I made two sudokus for  WSC2011.
This is my 3rd sudoku from this genre, and it is easier than my last Daily League Sudoku.
Have fun!

Rules for Rossini Sudoku

Standard Sudoku rules apply.
The arrows indicate that the nearest three digits in the row (column) are in ascending or descending order (increasing towards the direction the arrow is pointing towards). If there is no arrow outside a row/column, the nearest 3 digits therein cannot be in either ascending or descending order.

nr. 943 - Daily League Sudoku - Secret Code Sudoku

I'm not sure that anybody recognized it, but my last 2 sudokus were totally same.
First I made the Product Sudoku that I found a bit hard. So I change the clues into Quadruple, and I published it. But it was solved so quickly, so I tried the original version, too.
It's intresting that the product version is 8x harder.

Today sudoku is based on my Mastertrio puzzle which appeared on the WPC2011.
I can't determine its difficulty, but it's tend to be hard.
I hope you will enjoy it.

Rules for Secret Code Sudoku
Standard sudoku rules apply. Moreover find out the 4-digit secret code. Digit repeting is allowed in the code and the order of digits is not relevant. Some intersection contain a smallnumber. Each small number denotes the number of digits around it that are part of the code.
For instance if the code 1,3,3,4 and the number  3,4,4,7 has 2 matches: 3 and 4 are common.

How to solve Radar? II.

I show a possible solving line for nr. 944 - Radar puzzle.

First I mark the walls between 2-3 and 3-4 clues as I mentioned before. Then I mark the same clues next to edge. Don't forget C5-C6 next to the wall.

As always I start the solving eith the largest numbers. In R10 the clue in 9. There are 12 cells there, but because of the walls at least C4 or C5 is empty. and the C9-C10 pair is same.
So R10C2 and R10C11 cannot be empty.

Similarly R2C7 and R11C7 are part of a rectangle. Then we can use the same-edge trick. Moreover R10C7 is marked, too.

Then I check the small numbers. 2s and 3s have the advantage, that all cells are in in group in that row. 

We can mark many empty cells using these small numbers and the walls.

Such as R3C5 then R3C6 (same clues) and R3C9.

Then the top of C5 and C6.

R9C5 and R9C6 because of the 3 marked cells in the bottom of C7. The cloud in R1C7 continues to right.

R3C4 must be empty because of the same clues in R1-R2.

R12C4 is empty then R11C4, as well.

In C10, R3 is empty (C11 and C12 are same), then R1-R2. Moreover R9 is empty too, then R9C11-R9C12. Now the cloud in R10C11 continues to down 2 cells.

 

Now a trick in C10. The 3 cannot be in the top part. Because 7 in C11 cannot be 3+3+1.

And similarly R3C11 is empty. Now we can finish the whole bottom part.

Let's finish the puzzle. 6 in C8 cannot be 3+3 because of the 4 in C9. So R3C7-C8 are empty. And R4C7-C8-C9 are filled. This was the last relatively hard step.

nr. 944 - Radar

This is the next part of my Radar tutorial.
The description of first trick, and the solution of example puzzle has already posted.

Now let's see the second trick, and a new practise puzzle.

If there are a 2 and 3 clue next to each other there is no rectangle that can part of both rows. 
Similarly if there are a 3 and 4 clue next to each other there is no rectangle that can part of both rows.


Because of every rectangle is at least 2 units wide. If a clue is 2 then there is only one 2-wide rectangle in that row. Similarly if a clue is 3 then there is only one rectangle in the corresponding row.
So a 2-wide and a 3-wide rectangle cannot be same.

Similarly a 4 clue can be a simple 4 or 2+2. It cannot part a 3-wide rectangle.

First I check if there is anywhere these kind of clues and I draw a bolded line between the two rows. It is a wall. These walls divide the grid into subregions.

In the next practise puzzle it is needed to use this trick and the previous one, too.
The biggest number is 9 in a 12x12 grid. There are 3 empty squares in that row, which seems too many.
But for instance there is a wall between R3 and R4.And it means that R3C7 or R4C7 is empty or both of them. These walls make it possible for the puzzlemaker to use a bit smaller numbers for starting.

Next time I will show the solving steps of this puzzle.

nr. 945 - Daily League Sudoku - Product Sudoku

My next puzzle in DLS series is much harder than the previous one.
This kind of sudoku is enjoyable for me, although the starting steps are quite boring. i.e. counting the prime factors of each clue.
Hence I added a pdf in which Ihave already did it.
If you like the math puzzle, but this one is too big for you, just visit my old site for easier Magic Squares with products.

Rules for Product Sudoku:
Follow classic sudoku rules. At some intersections of two crossing grid lines, a number is given. This number show the product of digits in the four adjacent cells.

The sudoku in pdf

How to solve Radar? I.

I show a possible solving line for nr. 946 - Radar puzzle.

First I marked the trivial empty squares (rows where the clue is 0), and I marked the same clues next to the edge or empty rows.

Then let's check the biggest clues. The are two 9s. C10 seems better, becase there are two marked empty cells while in R3 there is only one.

So C10 contain10 unmarked cells and 9 are filled. We can make the simple deductions.

Now we can use the trick. R1C10 and R9C10 are also filled.
So in C10 there remains 2 unfilled cells, R4C10 and R12C10.
Because of the 7 in R4  R4C10 cannot be empty.
We can fill the whole C10, then easy to fill the whole right side.

Now lets check the biggest clues again. Try to find rows/columns where there are N empty cells and N-1 are filled.
These are R3 and R11-R12.

Now we can use again the trick. And mark some cells in C1.
Then there are some simple deductions again such as R3C6 cannot be empty because then it is not possible to finish R2.

So finishing this puzzle isn't too hard.

But I want to show one more thing.

In C1-C2 there are 7s. It is an odd clue so there is at least one rectangle with odd width in this column. It can be just 3 width.

And clues in R9 and R10 are same, so it cannot be in the bottom part. Just in the up part.
Clues in R1 and R2 are also same. So it can be just in R1-R2-R3.

This is the way how it is possible to use the same clues trick.

nr. 946 - Radar

This is the first part of the (mini) series that will show the tricks of Radar puzzle type.
Let's see the first trick.

If the first and second clue is same on any side, than the first and second row is totally same.
The same is true, if there is 0 among the clues. And its neighbour and its second neighbour is same.

This is a simple consequence of the rule that every rectangles is at least 2 cells width.
So if there is a shaded cell in first row it will continue in the second. And the two clues are same, so there is no more shaded cells in the second row.

Here is an example which use only this trick.
For instance if R3C1 is shaded then it is trivial that R3C2 is shaded too.
Because of the trick the inverse is also true.
If R3C2 is shaded then R3C1 is shaded too. 
This is not trivial, but it is not a too difficult consequnce.

Another example is that if R3C2 is empty then it is trivial that R3C1 is empty too.
But the inverse is also true.
If R3C1 is empty then R3C2 is empty too.

First I check both sides of the clue and mark this pattern to not forget to use this trick.
In this puzzle there are 4 places where 1st and 2nd clue are same. But R6 and R7 won't give any extra informations because of the zeros.
Next time I will show the first steps of this puzzle. 

nr. 947 - Radar

Radar is one of my favourite puzzles. It's a well-known genre, but it's not especially popular recently.  Hence I will publish some puzzles, and I will share some solving tips.

I was thinking when I can say that this is a trick of the puzzle types.
I think  anything that more then a simple deduction is trick or pattern.

Such as in a Yin and Yang puzzle when in a 2x2 area there are 3 white circles then the 4th is black is just a simple deduction. But the edge connection is a trick.
Of course it is consequence of rules, so it is a logical deduction, but not a simple deduction.
My first 4 Yin and Yang puzzle on the Beginner Contest were solvable without any trick, but it is more faster if you use the tricks in trivial puzzle too.


Today I publish the 0th puzzle of the series. I call it 0th puzzle because it is solvable with simple deductions.

For example if there are N empty cells in a row, and it is required to fill N-1, then it is a simple deduction that the 2nd cell from the side cannot be empty.
Or if the clue is 3, then there is only one cloud in that row which is 3 cells width.


Normally I like creating 10x10 puzzles without given cloud parts. But when I make a trickless one, it is better to give some elements and to use a bigger size.

Rules for Radar

nr. 948 - Daily League Sudoku - Quadruple Sudoku

This is a familiar sudoku variant. I think it is one of the easiest where there is no given numbers.


If you want to solve this sudoku online you can do it tomorrow at SudokuCup.

Rules for Quadruple Sudoku:
Follow classic sudoku rules. At some intersections of two crossing grid lines, a set of four numbers is given. These numbers must be placed in the four adjacent cells.

nr. 949 - Yajilin

If you missed my Yajilin puzzles, here is one. It has medium difficulty. Enjoy!


Rules for Yajilin

nr. 950 - Battleships

 Simple (?) Battleships puzzle with only few clues, and with some kind of antisymmetric pattern.

Rules for Battleships

Solving tip - Minesweeper

This is the explaining of my previous Minesweeper post. I wanted to write it a bit earlier.
LMI Beginner Contest has ended 2 weeks ago. Last page of IB contained this link to help the new solvers:
2. Steps to solve minesweeper in EverGreens 1
http://logicmastersindia.com/t/?tid=77

This kind of dividing trick is relatively familiar in Minesweper puzzles. So I thought my set couldn't be full without at least one puzzle that use it.

This was the hardest normal Minesweeper. But I dodn't want to build the whole puzzle only to this trick. So it is mostly solvable without using the dividing.  Hence I don't think that too many people used it.

As I said many Minesweeper puzzle use this trick. Namely:
If you can find distinct regions that use the given number of mines then all remaining cells should be empty.
The main question is: jhow should I know that I have to search regions or solving the puzzle on normal way. Of course there isn't exact answer just some rule of thumb.

This was the 6th puzzle on the contest:

In my opinion in minesweeper puzzles very important the interaction between the clues. So that there there are many clues next to each other ortogonally or at least diagonally. If there are wholes between the clues it is a signed that you can use the dividing trick.

In this case the regions can be the followings:

 

The number of mines in green region is 20, so all white cells are empty.

Moreover, the 6th puzzle contained less mines than the previous puzzles. (30 vs 20)  this is also a sign for using the trick.

Now let's see the posted Minesweeper puzzle. 

In this puzzle the number of mines seems normal, and the clues are close to each other.  But there isn't any trivial starting points. This is the 3rd sign.

So let's try to divide the grid. The sum of subregions should be 30. So try to choose as big numbers as possible, and the regions should be distinct so I tend to choose numbers next to the edge. We can choose both 5s. Then 1 and 2 next to the edge. Then the three 3s in Row 6 and Row 9. And the 2s near to the corner.

 

The sum is 26. We need 4 more. But there is only one  for distinct region. However if we choose the 4 in R5C2 then it has at least 3 more mines. Finally the 4 in R7C8 has 3 green neighbours so it has at least one mine in the white area.

 

We found some regions that contains exactly 30 mines.
So all white cells are empty and the orange regions use the minimal number of mines, so the intersect og green and orange regions are full of mines.

 

 

Now it is a more easier puzzle. With some easy steps such as 1-2 in top-left corner. Or 2 in R9C1 with only 2 empty squares. Or 4 in R4C7.


In this puzzle there wasn't any easy starting point. But sometimes there are some easy steps then it is hard to  continue the solving. In this case you should think about the region-dividing.

Sometimes you can't make regions with the exact number of mines, but there are only some mines on the white area. In this case the regions can help to mark some empty cells or just solve the puzzle.


Rarely the regions work on inverse way. This means that you should find regions which use the minimal number of mines and all remaining cells contain mines.

In this nr.289  puzzle contain only 10 mines, but the clues are all really low. After some basic steps, it is possible to make regions so that the whole white region is totally filled.

nr. 951 - Daily League Sudoku -Tight Fit Killer Sudoku

This sudoku is the combination of Tight Fit Sudoku and Killer Sudoku.
All rules of these two genre are valid. Namely:

• Fill in the grid with digits from 1 to 9, so that each row, column and bolded-line region contains each digit exactly one.
• Each single cell contains exactly one digit, and each cells that divided by a line contains 2 digits; in these cells the smaller number must go above the larger number.
•  The digits within a dotted-line sub-region must be all different.
• The given numbers indicate the sum of digits in the corresponding sub-region.

I hope you will enjoy this funny hybrid sudoku.

nr. 952 - Minesweeper

My Beginner Contest on LMI has just finished. Now I can't write a long summary.

I post a Minesweeper puzzle which is harder than last normal puzzle on the competition.

In the next post I will write about its solving tecqnique. Now here is the puzzle without any comment :)

Rules for Minesweeper

Rules: Minesweeper

Place the given number of mines into the empty cells, so that each digit represents the number
of mines in the 8 neighbouring cells.

nr. 953 - Year of Snake

Normally the Hungarian Puzzle Championship consists of 3 rounds. 2 mix. For instanced Classic and less Classic and a bit special. I made this puzzle in 2011, a combined snake puzzle.

 It was 50 minutes long and 4 people could finish it. Don't forget that the best Hungarian solvers didn't participate, because they made puzzles for WPC.

I tried to construct it so that many partial points are available. I think it was an enjoyable round, at least for those who like snake puzzles :)
The puzzle and its example are found in pdf.
I don't publish the solution of example puzzle this time.

Thanks to Zoltan Nemeth for translating.


This round consists of 6+1 Snake puzzles. The six puzzles in coloured grids can be solved on their own. Solving any two adjacent coloured grids allows for the white area between them to be solved.                                                   
                       
Top left and bottom right puzzles                               
Classic snake                               
"Basic snake rules: Draw a snake into the grid which consists of horizontal and vertical segments, never crosses itself and never touches itself, not even diagonally. The head and tail are given as grey circles. The snake avoids black cells.

Classic snake rules: Numbers around the grid indicate the number of cells occupied by the snake in the given row/column."                               
                       
In the sample, top left and bottom right puzzles are classic snakes.                               
                               
Top centre and bottom centre puzzles                               
Finnish snake                               
Basic snake rules apply. The snake goes through all white circles.                               
                               
In the sample, bottom left puzzle is Finnish snake.                               
                               
Top right and bottom left puzzles                               
Graffiti snake                               
Basic snake rules apply. Number groups around the grid denote the cell groups in the given row/column that the snake does NOT occupy, in the order they appear.                                
                               
In the sample, top right puzzle is Graffiti Snake.                               
                               
White puzzle                               
Minesweeper snake                               
The snakes in the six coloured puzzles are all parts of a giant snake.                               
The giant snake's head and tail are given as grey circles in the middle white zone. It enters and exits the coloured puzzles at the grey circles (i.e. the heads and tails of the small snakes).                               
                               
In other words, the giant snake can cross the dotted boundary lines but not the thick ones.                               
Basic snake rules apply to the giant snake. The no-touch rule applies even if one segment is in a coloured area and the other in a white one. There may be multiple segments of the giant snake in the white area.                               
                               
Numbers written into the black squares denote the number of cells occupied by the snake (out of the 8 surrounding cells connected horizontally, vertically or diagonally).                               
                               
No such minesweeper clues are located adjacent to any of the coloured puzzles, therefore they do not provide information to the small snakes. This applies to both the sample puzzle and the competition puzzle.                       

      
                               
Year of snake in pdf

nr. 954 - Daily League Sudoku - Product Squares Sudoku

 I made this sudoku some month ago. My solving time now is 15 minutes, let's see if anyone can solve it under 5 minutes :)

Rules for Product Squares Sudoku:
Standard sudoku rules apply. Additionally for each gray squares the bottom cells contain a two-digit number which is the product of the numbers in the two upper cells.

For instance if the top numbers are 7-9 or 9-7 the bottom is 6-3 (stricly in this order).

nr. 955 - Mini Sudoku

I made this puzzle for last year's hungarian Sudoku Championship. The original version was too hard, so I added some more extra numbers and signs. The final version was enough easy.

6 player could finish it under 35 minutes.

I post here just the original one. The puzzle is downloadable in pdf.

Since the example is a valid puzzle, as well. I won't publish its solution.
Have fun!


Zoltán Németh translated the rules.

This round consists of nine Sudokus of size 6 that are connected through relational signs. Standard Sudoku rules apply in all these puzzles. Some of the small Sudokus may have a unique solution on their own, while others need neighbouring puzzles' information to be solved.

Relational signs are located between the puzzles, as in the sample. For halved Sudoku, the relational sign should be applied for the digit within the cell even if it is in the half cell away from the sign.

There is no other connection between the puzzles, e.g. the shape of tiling does not need to match between puzzles 4 and 6, even if in the sample they happen to look alike.

1.Top left: Irregular Sudoku

The boxes are not necessarily rectangular.

2. Top centre: Thermometer Sudoku

Starting from the bulb of a thermometer, its digits must strictly increase, although not necessarily by one. E.g. 1,2,4,5 could be a valid thermometer.

3.Top right: Neighbours Sudoku

A dot denotes that the difference between the digits in the two edge adjacent cells is one. All such dots are given. In other words, where there is no dot, the difference is not one.

4. Centre left: Half Box Sudoku

The grid is divided into areas of 3 cells each. Pair them to establish areas of 6 cells each such that these areas can serve as boxes for Sudoku rules perspective, allowing no digit to repeat. Each box has to be connected.

5. Centre: Diagonal Sudoku

No digit can repeat in either of the main diagonals. There are no boxes given.

6. Centre right: Tripod Sudoku

The boxes are not given and have to be restored. Wherever three segments of the boxes' boundaries form a T-junction, a dot is placed. There are no junctions where four such segments meet.

7. Bottom left: Kropki Sudoku

White dots denote that the difference between two adjacent digits is one. Black dots denote that one of the digits is twice the other. Wherever there are no dots, the two digits do not satisfy either criterion. There may be a white or a black dot between a 1 and a 2.

8. Bottom centre: Arrows Sudoku

Digits in a circle equal to the sum of digits on any arrow starting from that circle.

9. Bottom right: Halved Squares Sudoku

Squares that are halved also contain a digit in one of the halves; the other half remains empty. A number in one half of a cell does not belong to the area that contains the other half of the same cell.

 

Mini sudoku.pdf

nr. 956 - Yin and Yang

Another puzzle which originally I wanted to make for the team game. It's solvable logically, but enough hard. The second version was much easier and maybe it has a bit nicer design.

Rules: Yin and Yang

Place a black circle or a white circle into every empty cell so that all cells with black circles form a connected area and all cells with white circles also form a connected area. Circles in an area of 2x2 cells cannot all have the same colour.

nr. 957 - Regional Akari

Since my first Akari was too hard I tried to make an easier one. In this puzzle the main step is finding cells that can be lighted from only one region. So I used less number of regions, and I expected that then the puzzle will be easier. According to Bram this puzzle has similar difficulty then the privious one.

I used a bit different layout to emphasize the regular form of regions.
If you want to solve my last and easiest Regional Akari puzzle you can find it in the Team round file.

Rules for Regional Akari

nr. 958 - Regional Akari

Another extra puzzle from the team game of Polish Championship.
Bram chose me this genre, as well. I haven't created any Akari variation before, so it was an intresting challange. This was the first attempt, but the puzzle was too hard for the competetion.

Rules for Regional Akari

Rules: Regional Akari

Place one lightbulb in each blackbordered region, so that every cell in the grid is illuminated by at least one lightbulb. Lightbulbs illuminate all cells they can see in a horizontal and vertical direction. Black cells block their sight. No two lightbulbs can illuminate eachother.

nr. 959 - Haido

I took part in Polish Sudoku and Puzzle Championship last weekend.
And Bram and me made a team round for this event. Every information about this round is found here.
Including my puzzles which I won't post here.

As Bram mention it in his post we played a game. I chose 8 puzzle types for him, and he did the same. So I had to make a Haid puzzle. I like skyscraper puzzles, it was intresting to make a puzzle from this relatively new, but simple variation.

I had some problems with finding a nice design, finally I just made a simple symmetrical puzzle. I made this hard puzzle while trying to make an enough easy for the competition :)

Rules for Haido

Rules: Haido

This is a Skyscrapers variation.

Place the digits in the given range once in every row and column. The digits represent skyscrapers of that height. The clues on the outside indicate that the building of this height is visible in that row or column from that side. Larger skyscrapers block the view of smaller ones.