The puzzle is a number puzzle named "Number Place" which had saled by an American Company named "Dell Magazines" (http://www.dellmagazines.com/) since 1979. It had gained in England at first and in worldwide popularity in 2005 as named "Sudoku". For this reason, There are many people who're misunderstanding that Japanese created it.
It's a number puzzle where you place a number from one to nine into 81 cells, avoiding duplicates into each row, each column and each 3x3 region.

If it's the first time you know the rule, I recommend you to play the software be set to a level "Practice". It may be enough at once, instead, you would be bored in a middle cause the level is too easy. And never set it "Practice" again.



Features are descripted at the outset. It may be easy to use the software intuitively due to have a look at the menu though, I shall write an overview of functions at here.
In depth at next chapter.

As pulldown menus of 'Board', erases quiz and erases only answers and candidates. data.

As pulldown menus of 'Puzzle', creates a new puzzle, hand-building a puzzle and load its puzzle.

As pulldown menus of 'Solve', solves a puzzle no matter how hard.
It has two methods as 'Pencil Marks' and 'Backtracking'. Backtracking is a forcefull method and it can solve any puzzle no matter how hard.
As for candidates analysis, it changes the analysis depth cause a cell with single candidate should be hidden. Thus there may be cases of no candidate expressed, even if by a shallow analysis, in case of easy puzzles.
And judge whether a puzzle is solvable structure or unsolvable, single answer or multiple answers.

As pulldown menus of 'Option', sets difficulty level of a puzzle, settings about default parameters at boot of the software.
As a menu of 'Settings', selects how to express mistakes, resets answering and candidates.
As for express mistakes, selects one of 'No Express', 'Visible Mistake' and 'Absolute Mistake'.

As pulldown menus of 'File', load and save puzzle data.

Those may be easy to use due to try though, will be explained in depth at next chapter.




ver.1.00.00 on --th ---- 20--
-- 1st Release

Due to 'Clear All Quiz Data', all board numbers will be deleted.
Due to 'Clear Solving and Candidates', board numbers will be deleted except quiz.
Due to 'Clear Candidates', candidates numbers only will be deleted.

After outputting or loading the quiz, the answers are entered by tapping the 'Number' button at the bottom, selecting a number and tapping on the board.
Candidates can be entered in the same way: up to eight candidates can be entered in one cell. If you want to remove a particular number from the candidate list, you can do so in the same way as you enter the number.



Due to 'New Puzzle', a puzzle is created.
Default level is set as 'Advanced' at boot, which could be exchanged by Preference menu.

A puzzle created by the software can be saved to a file by 'File / Save'.
Due to 'File / Load', a puzzle will be loaded.
At the Save, the status of unanswered, in progress or answered is automatically detected and the status is also recorded, which is reflected in the status at the time of Load. In other words, you can save a quiz in the middle of an answer, and then continue with the rest of the quiz by Loading.

Due to 'Preference / Level Setting', difficulty level is changed. And the default level at boot is also changed due to 'Default Settings' under 'Option'.
'Extra-Terrestrial' intended as a most hardest level was disabled cause it did not arrive at the goal. But the software has seven levels and 'World Class' puzzles are not harder than Inkala2012 though, they are harder than Inkala2010. I feel that's enough for the satisfaction level.



Due to 'Hand-build Puzzle', a puzzle can be created by hand-building. The puzzle created can be saved to a file.

There are several functions enabled during the hand-building, multiple answers or single answer, solvable structure or unsolvable, analysis and express candidates, deleting candidates, and solving (the Pencil Marks, the Backtracking). Those might be useful for hand-building a puzzle.

Next, it's finished to enter the answer into all cells and push the button scripted 'finish'.


Also, a correct answer could be input and be expressed due to solving (the Pencil Marks, the Backtracking) without inputting point by point. As for the rest, due to push the button scripted 'finish', the puzzle would be created with the answer. It depends on the puzzle whether the answer is single solution or one of multiple solutions.

It's possible to check solvable structure or unsolvable.

After tap the 'finish' button, it will return to menu and tap 'Load A Hand-build Quiz', then the quiz will deploy on the board.
It's able to save the quiz to a file after load the hand-build quiz.



The software can solve any puzzle no matter how hard.
Inkala2012 claimed as the world's hardest sudoku puzzle (mentioned later) is not exception. Puzzles with multiple answers can be solved even they show another answers at each time.

Due to 'Show Candidates', analyses candidates. Candidates are just hints and not be expressed in case of single candidate.
That's inconsitency cause each cell has only one candidate except puzzles have multiple answers. Therefore, candidates are marked out due to change the depth of analysis by difficulty of puzzles. As for too easy puzzles, no candidate is expressed even if the depth of analysis is shallow.

Due to 'Open Answer', expresses the answer. i.e. resign. Of course in case of existing the answer data.

'Pencil Marks' simulates a normal method as determined hand-solve method, and it can solve almost hand-made puzzles appered on publications in a moment. However in case of puzzles with multiple answers it ends leaving the region off.
And it can not solve puzzles which has deep recursives, for examples, sometimes puzzles created by 'Expert' level and almost puzzles created by 'World Class' level of the software.

'Backtracking' can solve any puzzles no matter how hard, even if the depth of recursive is very deep created by 81 cells. In addition, really a puzzle aside, it can solve any puzzle with multiple answers even if it has few hints, without respect.

'Backtracking' is used a simple technique in random chance for solving quickly. As the result, it takes random time to solve a same puzzle. It takes in a moment to solve the world's hardest puzzle and in another time it takes several seconds to solve the same puzzle.
It's a challenge for the future to make it to be optimized and to be efficient stable function.


Due to "Check Solvable", it's able to check whether a puzzle is solvable structure or unsolvable. It's recommended to check it in case of a puzlle hand-built.
There are unsolvable puzzles even if the hints seem to be based on the rule. A sample file of unsolvable puzzles named "unsolvable_xx.np" is located in the folder "sample" which is never solved even by the backtracking.

Due to "Check Multiple", it's able to check whether a puzzle has multiple answers or single answer. At the same instant, it checks the solvable structure.
This fuction could be done during hand-building. And, the function analysis and express candidates was also enabled during the hand-building. In the case "Reset Solving" deletes only candidates. Those might be useful for creating a puzzle.



About 'Preference / Settings', The software has three selections for express mistakes.
Due to 'No Express', shows nothing.
Due to 'Visible Mistake', shows appearance mistakes, rule-based mistakes, as a red font.
Due to 'Absolute Mistake', shows mistakes based on the answer registred, as a red font. That's limited in case of existing the answer in the data. A puzzle data without the answer can be created by hand-build method.
It's not always true that 'Absolute Mistake' shows an absolute mistake, it's just different number to the answer registred. For an example, in case of a puzzle with multiple answers.
Default of express is 'Visible Mistake'. And the default express at boot can be changed due to 'Default Settings' under 'Preference'.

Due to 'Default Settings', changes parameters at boot of the software.
About difficulty level and express, quality of puzzle creating, confirmation for save, those can be changed as preference in a dialog.

The images below are from the Windows version, which is functionally identical to the Android version.



Puzzles created by the software have only single answer avoiding of multiple answers to make sure.

A puzzle with multiple answers is not so difficult but often result in easy. However it's need some way of assumed method in a process of solving. Could it be called puzzle?

It's not to be solved but to be found.

As a famous puzzle, Inkala2010 (right pictures are the puzzle and the answer) has multiple answers. Is that a black history for Dr. Arto Inkala?

I tried to solve the puzzle couple of times due to Backtracking Method (following three pictures). All of them are different to the answer released but there are no rule-based mistake. It always brought a different answer at each time. It seems to have lots of answers.




A right picture is Inkala2012. It becomes a great deal harder than Inkala2010. And it has only single answer. Incredible.



Already mentioned above, due to "Check Solvable" it's able to judge whether a puzzle is solvable structure or unsolvable. There are unsolvable puzzles even if they seem to be based on the rule. A right picture is a sample of unsolvable puzzles which file is located in the folder "sample".

As for this example, under pictures are results solved by the Pencil Marks after selecting and inputing one candidate in a cell.

A left picture is a result solved by the Pencil Marks after inputing 4 in a cell located at 1st row 2nd column.
A right picture is a result solved by the Pencil Marks after inputing 7 in a cell located at 1st row 1st column.
The Pencil Marks is a locally determined sequential method and so progress of the processing could be possible to break the rule only in case of unsolvable structure.




Books as puzzles collection, the internet and softwares. By far, it's recommended to get the puzzles from the internet.
Because, as follows


To put it another way, books as puzzles collection are almost subpar contents.

In early phase of the boom, I knew nothing at the time though, there were puzzles with multiple answers even if which were created by mathematicians. Some observers predicted that the composers on books did not make such a mistake. However, those days were gone.
The composers were just hand operators and they could not use solving methods except the Pencil Marks without their attention, and so it's easy to avoid to multiple answers.
There was a great difference as a sphere of challenge.

Nowadays, hints required minimum amounts had calculated for avoiding to multiple answers. The difficulty had been quantifiable due to calculate the depth of recursive dependencies. Of course, as Dr. Arto Inkala remarked, it's impossible to estimate the difficulty by a unified standard because that's depending on a solving method.
And, it's approximately same to devide several levels due to a certain criterion and to do due to another criterion. A first thing for users is possible to play at the level appropriate to them.

On the internet, there are lots of puzzles from novice class to very hard which could not be solved by a normal person. It could be reward for many users to be deep in between.
That's not existing in the books but the internet.
In the books as puzzles collection, there are only puzzles from novice class to intermediate class. Solving is just a simple task. They composers on the books don't know how to create a hard puzzle.


On the internet, recommended places are sites which have selectable levels. There are partly sites which create only easy puzzles though. Search good sites with the level appropriate to.
At sites which release puzzles on a regular schedule, there is a high possibility of finding high quality puzzles. Almost popular news-sites have a page of puzzles as that style.

examples as following URLs



How to create a hardest puzzle? How to solve a hardest puzzle?
It's easy to solve a hard puzzle by using a computer though, even by that, it's still very hard to create a hard puzzle.


(constructing ...)