Mastering Sudoku: How to Use Candidate Mode for Faster Solving

Are you looking to improve your Sudoku skills and solve puzzles faster? One helpful tool you can utilize is Candidate Mode.

We will explore what Candidate Mode is, how to access it in Sudoku, and the benefits of using it.

Get tips on how to effectively use Candidate Mode to solve puzzles, common mistakes to avoid, and how to practice using this mode.

If you’re ready to up your Sudoku game, keep reading!

What Is Sudoku Candidate Mode?

Sudoku Candidate Mode is the function in a Sudoku app that allows a player to annotate a digit in a cell to later try fitting in the cell as a solution. Candidate Mode is helpful on hard or evil level Sudoku puzzles because the candidate cells can help a player to quickly see possibilities that might otherwise be hard to spot.

The most common notation form is known as Candidate List or Pencil Mark writing. In this mode, all potential values that a cell could have are written in small numbers inside the cells of a Sudoku board. You then try out these options based on other numbers in neighboring rows, columns, and sectors.

Candidate Mode is used on desktop, mobile, and app versions of Sokoban puzzles by allowing the user to switch between modes by pressing an icon or a key while playing. On Exon Labs’ Socu Sudoku App for Android, the user can toggle candidate mode by clicking the excclamation mark icon on the bottom right corner of the game board.

How to Access Candidate Mode in Sudoku?

Candidate mode in Sudoku is available in sudoku apps by choosing the candidate mode on an open cell. To add candidates to input are the various ways apps have been incorporating the functionality based on how they feel it is easiest and most ergonomic way to utilize the feature.

  • Mobile Fuji Sudoku App: Tap on an empty cell and candidates will start showing as small numbers in the center of a large cell. Repeatedly tapping the number will add it to the candidates list to the side of the puzzle.
  • Fuji Desktop Browser Sudoku App: Tap on a cell to select it, and press c to show/hide candidates. Type a number followed by enter to add/remove from the candidates list.
  • Pure Ajax Sudoku: Tap on an empty cell. Then tap the white background of the number button to open up a candidate list.
  • New York Times Sudoku Online: After selecting a cell, click the center of the highlighted area (“Tap here for possible numbers”) to show or hide the candidate list. To add or remove a number, click the individual number box, then the center area again.

What Are the Benefits of Using Candidate Mode?

The main benefit of using Candidate Mode is that it helps you solve the hardest sudoku puzzles. Providing a visual reminder of the numbers that can fit in each cell allows you to keep track of your thought process in complex puzzles where multiple paths may present themselves, but only one will be correct. Additionally, for many people new to the game it can be used as a learning crutch to help visualize potential next moves.

How to Use Candidate Mode to Solve Sudoku?

To use candidate mode to solve Sudoku, write the possible missing numbers in cells that fit based on blocks, rows, columns. Subtract those common numbers from other cells in rows, columns, 3*3 blocks, and mark those as ineligible candidate cells. Consistent application of the eligible/ineligible pattern will eventually fill out all remaining numbers and resolve the puzzle.

Identify Possible Numbers for Each Cell

Identifying every possible number for each cell is the foundation of using {Candidate Mode}. {Candidate Mode} provides a way to keep track of these possibilities through the use of candidates. A candidate is any possible number that can make a cell a solution. For example, a cell that is part of a box-line intersection would have two candidates remaining, one in the {Box} section, and one in the {Row} section. By assigning 4 as the designated candidate in the {Row} section and 7 in the {Box} section, one can see that the cell at the intersection must be 4 or 7 and the cell is denoted as such.

Start with the top left and move cell by cell, marking all possible numbers. If the cell only has one possibility, it becomes the solution for that cell. The possibility notation system is as follows: If 4 and 8 are possible solutions for cell {C2}, candidates for {C2} are shown as {48} in the bottom {Result} field.

  • These are the rules for identifying possible numbers and candidates:
    • A candidate can be any number from 1 to 9 which does not have any conflicts.
    • There can be zero, one, or many candidates per cell.
    • A cell has zero candidates when all the numbers is obscured by other numbers making the cell impossible to definitively solve. This would only happen when the initial puzzle is being set.
    • A cell has only one candidate when there are no other numbers that prevent any possible numbers from occurring. 8 of its peers must have a number to conflict with its candidate to ensure no two cells in the same box, row, or column have the same number. This means there is just one possibility left, and it is essentially the candidate.
  • These are the general points to consider while identifying possible numbers and candidates as needed.
    • If you designate a cell number candidate in one of the box-section, row-section, or column section, be sure not to designate another number for that same cell in the other modes.
    • If there is a direct contradiction where a candidate can be only 3 or 7, and one of the peers like {A1} made it 3, then the peer like {C3} of the contradiction cell is 3.
    • After candidates have been noted, it is useful to use pencil marks as they are available in every cell when notes are enabled. This allows for candidates to be viewed across the board, not just in the final results section.

You will be forced to logically solve most cells before becoming more comfortable with determining possibilities.

Use Elimination Techniques

Elimination techniques are used to remove wrong candidates from a cell to reduce the possibilities. We use candidate mode to keep track of those possibilities temporarily until we reach a solution. See these two examples for usage.

This is the before-shot of a sudoku puzzle that Daulyan shared on Reddit in which candidate 3 was in every row and column except rows 1, 7, and 9. Therefore we could eliminate candidate 3 from the highlighted cells. This is how the grid looked after eliminating 3.

Use ‘What If’ Scenarios

What-if scenarios are when a candidate is true, it is only unknown. If after filling a square with a specific digit there are multiple candidates for its neighboring squares, try using different candidates for the original square to eliminate them. This is especially useful in guessing scenarios where candidate usage is heavy, as it can reduce possible solutions without as much effort as attempting to directly solve by candidate choices.

What Are the Common Mistakes When Using Candidate Mode?

The following are the common mistakes when using candidate mode in Sudoku:

  1. Forgetting Candidate Mode is on: If a digit is clicked in Candidate Mode, it remains on the board after deleting a candidate. If one accidentally switched into Candidate Mode but does not want to keep it on, it must then be manually turned off.
  2. Forgetting to switch Candidate Mode on: When solving difficult Sudoku with multiple possible candidates for different squares, Candidate Mode needs to be used to record potential answers. If the small numbers from 1 to 9 do not appear on the cells when there are multiple possible answers, this will be much harder to keep track of.
  3. Not utilizing the X-wing technique: In some Sudoku puzzles, the X-wing method is capable of eliminating a candidate from further consideration. You might be able to use the following exercise to solve:
  4. Not flipping between pencil and candidate mode: Some candidates think that the X-Wing rule for eliminating a solution is not a valid strategy to make a pencil mode move. This applies to Sudoku puzzles with many candidates in each box throughout the board. To avoid mistakes, they have to constantly switch between pencil and candidate mode, especially for split-house strategy.

One of the most common mistakes sudoku players make when using candidate mode is not switching candidate mode on and remembering to constantly switch between it and pencil mode during split-house strategies. The AI assistant uses candidate mode when solving sudoku but does not have the capability to switch this mode off when simply playing a sudoku game.

Not Updating Candidate Numbers

If you do not update candidate numbers in candidate mode, then Candidate Mode stops being effective. In Candidate Mode, a puzzle with 25 or more clues will contain 8 or less pairs of candidate numbers, and a puzzle with 20 or less clues will contain 4 or less pairs of candidate numbers.

Although updating candidate numbers in all cells may seem overly meticulous as the number of conflicting clues adjusts candidate values, others say this accuracy is essential. If you want to see a wider range of possible moves at a given time, updating candidate numbers becomes even more important. Regularly updating candidate numbers makes solving an ordinarily difficult puzzle even simpler.

Adequate candidate mode may not be beneficial in its new, improved use of the feature, in which more than 3 values appear in each cell. If candidate mode stops complying with this specific numerical structure, the feature will not help. And, with this new structure, semasis is essential in finding required number values within the complex math of a sudoku puzzle.

Not Using Elimination Techniques

Not Using Elimination Techniques in Candidate Mode is the correct second method of How Not to Use Candidate Mode in Sudoku. Elimination techniques are the key strategies behind sudoku, which allow the proper assigning of correct numbers, based on finding where a number lies in a 9×9 grid of rows, columns, and squares.

For example, there are only two cells in row 3 that can contain the number 9. Applying candidates to this row highlights these cells as possession candidates.

The sub-set technique for candidates is particularly true of using Naked Pairs. For example, employing candidates and then elimination for row 9 in this sudoku puzzle, you can quickly find the pairs 36, 38, 45, 47, 54, 56, 75, and 78 as they are the only numbers that can be placed in the highlighted cells.

As practice, be sure to begin each new sudoku puzzle at the beginner level so as to train your mind to apply these techniques. If you jump to Expert, you may quickly unravel the mystery of the puzzle, but you will not acquire the techniques to enhance your playing skills.

Not Using ‘What If’ Scenarios

‘What if’ scenarios are a common technique for advanced sudoku solvers trying to identify candidate mode attributes. What if scenarios are created by means of multiple branches from a particular choice before a contradiction or solution is reached. By turning one of the candidate mode mode cells into a real cell, relationships can be better understood and constraints identified to help solve other cells. Michael Mepham of the Independent UK Sudoku Embasy notes that this work can be done by hand, using a pencil and eraser to make temporary marks in cells to act out possible outcomes, or by notebook depending on your preference or experience. A candidate mode at the beginning allows you to evaluate several options and conduct many different hypothetical scenarios which may require a long time and/or paper/pen intervention.’

How to Practice Using Candidate Mode?

You can practice using Candidate mode by following these steps. Before Candidate mode, annotate all possible candidates on the entire Sudoku board. Use cues to identify shortcuts such as ‘Scissor cells’. Erase candidates that are now eliminated based on new move knowledge and repeat the process. Good Sudoku recommends an expanded Candidate view that fully covers the board. However, a selective Candidate mode or individual Candidate cells can help in quickly checking guesses or possibilities based on different move knowledge being applied.

Start with Easy Puzzles

Starting with easy puzzles solidifies the basic logic required for the solution.

Applying candidate mode will help because you can correct any missed moves easily. Make sure you have moved through the easy sudoku puzzles so you can correctly identify patterns quickly. Once you feel comfortable you are applying candidate mode effectively and quickly, try adding puzzle difficulty. Test yourself to make sure you are truly utilizing candidate mode and not just filling in boxes to satisfy the algorithm.

Keep trying new methods to apply candidate mode for subsequent puzzles, as one method will frequently not work for all puzzles of the same difficulty. Almost all sudoku apps and puzzles allow you to see the solution path. If you feel you are stuck, look at the solution to see which candidate you missed, or if another digit has been solved.

Gradually Increase Difficulty

Candidate mode is a tool used to track which square of a Sudoku grid can accept a specific number as a possibility. Candidates exist at every difficulty level, but they become more prevalent and necessary in higher-difficulty games. If you are new to them, begin to increase difficulty gradually. Don’t force them.

As you get faster and more accurate at notating and tracking the possible candidates, you can make more complex strategies. At the expert level, more extreme techniques can be utilized when standard deviation is separated from the lower-quality strategies, such as when trying to solve Hardest Sudoku by AI Escargot. In short, there are practical advantages to using candidates such as increasing speed and helping solve harder Sudoku. But it can become a bit of a crutch to avoid working through possible strategies such as x-wings or swordfish. Avoid using candidate as a crutch at lower difficulties, remapping it towards the need for more accurate Sudoku brain training, and fluid solving at higher difficulties.

Can Candidate Mode Be Used in Every Sudoku Puzzle?

Yes, Candidate mode can be used in every Sudoku puzzle whether solving it on paper, a computer, a smartphone, or even in your head. Generating candidates by penciling them in on a physical Sudoku puzzle is always a useful exercise, even for the simplest of puzzles, because it helps one to identify possible moves, even if it doesn’t necessarily provide a definitive answer.

While most online and phone apps do generate and use candidates so players don’t have to take the time to pencil them in, some apps such as the New York Times do not offer the ability to jot candidates in squares. In these cases, the next best solutions are to use the inclusion rule to eliminate impossible options or to do a quick backtrack in their minds to watch moves play out to a few steps beyond the next choice.

How to Turn Off Candidate Mode in Sudoku?

To turn off Candidate Mode from the candidates screen, click again on the same square you have long-clicked and removed it. ***Click the “X” shape to close the Candidate Mode, not the “*** which is for clearing multiple cells at once.

Keyboard Input Mode in the settings allows you to turn off Automatic Candidate Mode when you switch between Cell and Candidate Mode. Click the “Refresh” button for the same feature once selected in the settings to save your changes.

Frequently Asked Questions

How to Use Candidate Mode in Sudoku?

What is Candidate Mode in Sudoku? Candidate Mode is a feature in Sudoku puzzles that allows you to take notes of potential numbers for each empty cell, making it easier to solve the puzzle. How do I activate Candidate Mode in Sudoku? To activate Candidate Mode, simply click on the “Candidate Mode” button located on the top of the puzzle grid. This will enable the feature for the entire puzzle. How do I use Candidate Mode in Sudoku? Once Candidate Mode is activated, you can start marking potential numbers for each empty cell by clicking on them. These notes will appear in smaller font inside the cell. Can I change the notes in Candidate Mode? Yes, you can edit the notes in Candidate Mode by clicking on the cell again and selecting a different number. This allows you to keep track of all possible options for each cell. How does Candidate Mode help in solving Sudoku puzzles? By using Candidate Mode, you can eliminate potential numbers for each cell as you progress through the puzzle, making it easier to narrow down the correct number for each cell. Can I turn off Candidate Mode in Sudoku? Yes, you can turn off Candidate Mode by clicking on the button again. This will remove all the notes you have made and allow you to solve the puzzle without the feature.

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