In order to smoothly jump through the documentation sections, use the "list" icon on the top-left side of the page screen.
- Introduction
- Prerequisites
- History & inspiration
- Walkthrough
- Future improvements
- Conclusion
- License
- Tools used
‘Sudoku World’ is an easy-to-use application for playing sudoku online. It is a browser game that can be played across all devices – from small size smartphones to huge desktops. Created in terms of accessibility and scalability, it holds minimalistic, low detailed design in order to work perfectly with almost any type of screen. Offers a customizable options to fit individual user needs as well as to make the overall gameplay more appealing. Consists of four difficulty levels that can be found, which complies with different players’ skill degrees. Hence ‘Sudoku World’ is an optimal choice for beginners, intermediate level players and for experts too.
‘Sudoku World’ rules are fully based on original 3x3 Sudoku regulations. It works the same way as magazine („paper”) Sudoku puzzles do. Nothing fancy here.
If You are not familiar with sudoku in general, or this is your first time encountering that kind of puzzle, please take a look at detailed Sudoku guide for an in-depth explanation of game rules, techniques and more.
There are a couple of requirements that need to be fulfilled to make sudoku solving experience the most enjoyable.
1) Stable internet connection – since it is a browser application, it works the same way as usual websites. That means You will definitely need constant Internet access. It does not necessarily have to be a very good connection (in fact, the app works fine even for weak ones), but consistency is the key.
2) Learn Sudoku fundamentals – as mentioned before, it is highly recommended to get a grasp of Sudoku rules and solving methods. Even if you feel like a veteran-level Sudoku solver, I still encourage you to check the detailed Sudoku guide (at least for its' comprehensively explained ‘techniques’ section). All methods covered there are essential in order to solve all kinds of Sudoku puzzles – from simplest up to the most complex ones.
Inspiration to create a sudoku application came spontaneously. Personally, I used to solve a lot of paper-version sudoku puzzles back then, when I had plenty of spare time. At the beginning of January 2022, I was having a conversation with my friends, and it turned out that many of them enjoy doing this activity too. Basically, it was a motivating factor to create a simple sudoku app that can be used by them. Despite the fact that the project was not scheduled by any means, a final action came real quick.
The Sudoku World project was initialized on January 23rd, 2022. The very first week revolved around creating an initial landing page and sudoku board template. The Sudoku engine was slowly being formed, but unfortunately all the work had to be postponed (personal stuff).
March 12th was the comeback date. From on, the trickiest part began. Many aspects that seemed to be obvious and straightforward, in fact became absolutely harsh to prepare correctly. The most significant improvements made were to generate a completely valid Sudoku grid and to create a mechanism that checks if Sudoku has just one possible solution. March was also a month to debunk all naive approaches in regard to developing Sudoku games generator. In the long run it completely shifted the direction of the application and moved it on the right track.
April and May were all about creating difficulty patterns. That was the most strenuous work to finish, simply because of implementing those methods into a game. Each technique involved developing a check algorithm (in most cases very complex) and also a lot of intense, case-specific testing, bug solving, etc. Ultimately, by the end of May, the final sudoku rendering pattern was introduced, so that all major engine-based functionalities were completed.
The very last chapter of ‘Sudoku World’ development was adding some extra functionalities to the game and adjusting the application for various types of devices. Starting from half of June, a pencil-mark mode, history travel and info tab features were created, followed by a lot of visual improvements for each application aspect. A cherry on top was preparing an error page (hopefully you will not be forced to see it).
Finally, ‘Sudoku World’ got deployed to production on July 27th, 2022. The live app version can be found there: https://sudokuworld.onrender.com/
This section is a guide through all functionalities ‘Sudoku World’ provides. You can follow along if necessary – here is the link: https://sudokuworld.onrender.com/
Note #1: This part represents the actual app state for version [1.1.0]. Any new feature added subsequently might not be covered there, so keep that in mind !
Note#2: Images used for this documentation represent the actual layout for laptops / computer screens. If you are using another device type, the layout may look a little bit different, but overall functionality remains the same.
First off all - the landing page. If you follow above link, that screen should appear:
Landing page contains all the customization that you can adjust in preffered way. It is divided into three different categories:
1) Select theme – here you can choose the color scheme of application. It impacts only the visual aspects of the game. According to the chosen theme, colors would be applied appropiately to all elements, with a slight exception of Reset view and Completion view. You can only choose one theme. Currently supported formats are light (sun icon) and dark (moon icon). The default value is dark.
2) Choose a difficulty – enables you to choose a desired Sudoku level. Possibilities are as follows: easy, medium, hard, insane (also known as ‘master’). Only one difficulty level can be picked at once. Default value is set to none, which means that one has to specify the difficulty level before playing. When chosen, a „Play” button appears, which allows you to play the game.
Very important note: In order to maintain reasonable Sudoku rendering time, choosing a difficulty is temporarily disabled. Even though picking a specific difficulty box increases the chance to receive a corresponding puzzle, getting Sudoku with the requested level is no longer guaranteed. To minimize the issue, a reset button allows you to quickly get another Sudoku puzzle. We are sorry for the inconvenience.
- Options – enables you add some extra features to the game. They affect only the gameplay. You can include as many options as you want. By default, all options are disabled (set to false). The following are available:
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Add Timer: When enabled, count up the time spent on solving Sudoku. Once the puzzle is completed, the total time is shown on the Completion screen.
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Tile backlit: When enabled, it highlights all the Sudoku cells that share the same row, column or 3x3 square, that currently focused cell belongs to.
Once you are done with the customization part, it is high time to play Sudoku. In order to do so, click the „Play” button (should appear right below the customization section).
Afterwards, you can see the Gameplay page, which will look similar to this:
It might look a bit confusing at first, but everything would be clear in a minute !
At the center of the screen, there is a Sudoku board. That’s the puzzle ‘playground’, which represents the current state of the game. To insert a number into a cell, you have to target it first. Simply click on the tile, and the cursor would appear right in this place:
Once the middle tile is targeted, it is possible to insert a digit there. As seen in the above example, the only number that we can place (according to Sudoku rules) is 8. Using right-hand side number box, let’s choose ‘8’ by just clicking on the appropriate tile:
Congratulations! That is how a digit can be inserted into a cell. You can basically rinse and repeat this process until you solve the whole puzzle.
However, mistakes could happen on the way. Whenever you find yourself in situation, where the wrong digit is accidentally put into a cell, there are two possible solutions:
The first one is to click on a „rubber”. That is the very last, rectangle-shaped box at the bottom of the number box. To make it easier to spot, it has been marked with a yellow color. Rubber allows you to quickly remove any number from a cell.
Alternatively, if you look at the above example – we want to remove this unnecessary ‘8’ from the top of the middle 3x3 square. The cell is already targeted. Apart from using rubber, it is possible to pick ‘8’ from the number box again. Instead of inserting ‘8’ anew, we will remove it from the cell.
For this specific scenario, you can follow a quicker approach. Since we are certain that the only correct number for the top-right cell in the middle 3x3 square would be 9, instead of removing 8, we can click on ‘9’ in the number box to replace an existing digit with 9. That is way more effective !
From now on, you should be comfortable with basic functionalities of ‘Sudoku World’.
However we haven’t covered the left-hand side section yet. That is called the toolbox, and contains several useful features (tools) that might be helpful in some specific cases.
An honorable mention here is the 'pencil-mark'. If you click on the pencil-icon box, you can notice some visual changes:
As shown in the above image, the pencil-marks' icon borders have changed as well as the rubber box, which has its background color modified. That means the pencilmark mode is now set up. Let’s take a look at below image to see what 'pencil-mark' tool is capable of:
Basically, entering pencilmark mode allows you to make some notes of possible digits that can be inserted into a given cell. In this example, the 3x3 square located in the top row, middle column is fully marked using pencil marks.
This feature becomes handy especially when dealing with more challenging Sudokus, which require a lot of memoization or using some complex techniques. Also, if there is a cell which contains just two or three possible digits, there is nothing wrong with just adding them as pencil marks.
Applying a pencil mark is as simple as for a digit. For this purpose, a number box is also used to choose a pencil mark number. In fact, adding, replacing and removing pencil marks works identical compared to digits.
However, there is one, slight difference. When entering pencilmark mode, there is no possibility to use rubber (note that the rubber box received a dimmed background color). In order to remove the whole pencil mark group from a cell, the most effective way could be escaping pencil-mark mode (just by clicking the pencil-mark box again) and then using rubber for a targeted cell.
All pencil marks are dynamic and adapts to your actions. That means, whenever a digit is inserted, each cell that shares the same row, column and 3x3 square would automatically remove these pencilmarks, which have the same number. To clarify, consider this quick case:
- Before adding a digit 1 to the targeted tile *
- After adding a digit 1 to the targeted tile (check top-middle and middle-right 3x3 squares) *
Toolbox also contains two fancy tools that look similar to each other. They are part of time travel feature, Combined together, allows you to freely move around the past actions you have done.
Time travel button that is closer to the left allows you to move backwards, while the one further from the left enables you to move forwards.
Whenever you start a new Sudoku game, as the above image shows, time travel buttons have their borders gray colored. For each of these tools it means they are inactive. Since we haven’t done any action yet, there is no way to move forwards or backwards in time by any means.
Once we make our first action, „go-backwards” button will receive its’ border color:
That means there is a possibility to move backwards. In this case, by clicking „go-backwards” button, digit ‘2’ would be removed from the board and because from that point there is no other action we can move back for, the button would become inactive:
Surprisingly, „go-forward” button has become active now, which means when we click onto it, we will put digit ‘2’ back into its’ place. Because there is no other recent actions to move forward for, now „go-forward” button would become inactive (turning its border to color gray), while „go-backwards” button from now will be active (changing the border color to green back again):
Time travel might be helpful especially when, after some actions taken, you notice a mistake that had been made before, and it is too late just to use rubber to correct it:
Take a look at the middle right 3x3 box for a moment. We want to insert a digit ‘2’ somewhere in here, but it seems like there is no possibility for that. It is due to a mistake made in one of the past actions. In the middle Sudoku row there is digit ‘9’, applied twice. While it might look as an easy fix just to trade places between 2 and 9 (see middle 3x3 box), it will cause another issue with Sudoku’s sixth column, which would have digit ‘2’ inserted twice. At this point, any further action that you will take might make the situation even more complicated than that.
Erasing the whole Sudoku board is some sort of solution, although far from ideal. Basically it will force you to start everything from scratch – even the parts you had done correctly before making that mistake.
Instead, you can make a good use of time travel functionality:
By pressing the very left time travel button, we were moving back in the game's history. Finished clicking exactly when digit ‘9’ was accidentally inserted. Now we can safely trade places between digits ‘2’ and ‘9’ and continue from this point:
Notice that once we actually make a change in one of past actions, „go-forward” button becomes inactive. Here is also a very important part to remember:
Modifying one of actions done in the past, would override game history, hence it will no longer be possible to retrieve actions that were done after the changed action.
To clarify: time travel buttons behave the exact same way how CTRL + Z and CTRL + SHIFT + Z keyboard shortcuts do.
Time travel feature might be useful if you would like to analyze your gameplay:
First off, make sure you are one action before completing Sudoku (do not finish yet):
Then, by using „go-backwards” tool, move all the way back to the very beginning:
And finally – use time travel buttons to browse through the actions made. As long as you will not insert any number to one of past moves, you can freely come back to the very recent action and finish the puzzle.
Last Toolbox feature to describe is the Info Tab. That’s the button with the ‘i’ icon. Once pressed, such screen should appear:
Here you can find some pieces of information regarding ‘Sudoku World’ application. This screen allows you to track the recent app version and its release date. There are also useful reference links – the first one redirects to the detailed Sudoku guide, the second one to this documentation.
As a side note, if you play Sudoku with a timer option included, this screen works as a pause button. It blocks the timer from running until closing the tab.
By clicking the „close” button at the bottom, you will return to a game with fullscreen mode enabled. If you wish to exit full screen mode, simply press the „Esc” button on your keyboard. For mobile device users, you need to press a „<” button at the bottom-right of the device screen.
At the beginning of this section, a reset button (‘New Sudoku’) was briefly mentioned. It minifies an issue regarding non-guaranteed Sudoku difficulty. It can be found right below the Sudoku board.
The sole purpose of Sudoku resetting is to let you receive the desired difficulty puzzle as soon as possible. Once the button is pressed (and you haven’t taken any action yet), old Sudoku is being replaced with a new, random one almost instantly. It is just a quick rendering time and new Sudoku is showing up.
Using the reset button still does not provide any warranty in terms of difficulty level.
I have done a quick research of how much time it takes to render 10 Sudokus with each difficulty. Below are the results (for every level there are three test cases):
10x Easy ~ 00:34 || 00:16 || 00:21
10x Medium ~ 03:51 || 02:07 || 05:14
10x Hard ~ 04:44 || 04:12 || 04:11
10x Insane ~ 01:11 || 00:31 || 00:55
Reset button has an in-built mechanism that prevents accidental clicks. When at least one action is already made, clicking on the button will make a dialog box appear:
Clicking the red „undo” icon on the left would exit this screen, keeping the same Sudoku with its current state.
After pressing the green „check” icon, a new random Sudoku is being rendered. That being said, all the progress made will be irrevocably lost, since this is a one-way operation (it is not possible to retrieve that Sudoku back).
Each correctly solved Sudoku invokes a Completion screen to show up:
If you included timer as in-game option, Completion screen would look similar to this one:
Clicking the ‘house’ icon on the left would redirect you to the landing (home) page, where you can change your customization and play the next Sudoku with currently changed options, theme, etc.
By clicking the ‘plus’ icon, a new Sudoku is rendered – with the same, previously adjusted customization. It works exactly as a „reset button”, however without a confirmation screen being shown.
While ‘Sudoku World’ has already received a bunch of updates, it cannot be denied that there are parts that still need some sort of improvements.
🎯 The major issue concerns non-guaranteed Sudoku difficulty. Picking a difficulty box from the Landing page only increases the chance to obtain a respective puzzle. The goal here is to update the rendering part, so that you can always get Sudoku with desired difficulty, and also it has to happen in a very short, reasonable time. At very least, increasing the chance of obtaining medium and hard Sudokus could be a significant improvement, since those types of puzzles are beyond the rarest ones to receive at the moment.
🎯 Last, but not least – options. Landing page still has just two options to customize, which does not seem like enough. There could be more of them, although it is a matter of brilliant ideas to implement a new customizable feature, which is an actual option - not something that every player has to click to make the gameplay enjoyable.
Patch 1.2.2 update
Those improvement tasks has been done so far:
✔️ Important change that needs to be delivered is preparing the good-looking layout for tablets. Those devices have the screen almost square-shaped, which stands as an exception to mobile devices, laptops and desktops, which screens are rectangle-shaped. On account of this difference, a new layout should be prepared across all Views in the application. That might mean creating a very individual approach, which could involve changing the position of elements, some sizing modifications and more.
✔️ Maximizing the grid size might make a huge difference for user experience. That is especially true for mobile device users. Portrait-oriented screens are quite okay in this matter (but still imperfect), however „landscape screens” have the Sudoku grid a bit too small. Restoring some space for Sudoku board would shrink adjacent – already spacious - sections (Toolbox and Number box) a little bit, so that playing Sudoku could be more enjoyable.
Well – that’s it. By now we have learned all the basic and advanced features ‘Sudoku World’ has.
Thanks for checking out the official ‘Sudoku World’ documentation ! If you would like to, you can also take a look at the changelog, which contains all recent updates for this application.
I would like to thank everyone who supported me during the development journey of ‘Sudoku World’. Also a huge shout-out to Handmark (‘Sudoku of the day’) for their inspirational sudoku-revolved website, which shares a lot of useful tips that ‘Sudoku World’ is based around.
This game has been made under MIT License. Follow this link for it's detailed content:
https://github.com/Martimex/sudoku/blob/main/LICENSE
© Martimex 2022