Master the Puzzle: A Step-by-Step Guide to Filling in Sudoku

Do you enjoy a good challenge that tests your logic and problem-solving skills? Look no further than Sudoku!

In this article, we will explore the rules of Sudoku, the benefits of playing it, and how to fill in the puzzles using various techniques.

We will also discuss common mistakes to avoid, tips and strategies for becoming an expert, for solving difficult puzzles, and strategies for tackling different types of Sudoku variations such as Classic, Killer, and Samurai Sudoku. Get ready to sharpen your mind and have some fun with Sudoku!

What Is Sudoku?

Sudoku was developed by Howard Garns, a freelance architect from Connersville, Indiana. He constructed the famous Number Place puzzles while confined to his bed in the back of Governor State Hospital at Springfield, the state hospital in Illinois run by the Department of Mental Health. This occurred between 1971 and 1979, after a California architect, Wayne Gould, saw a grid of Number Place Sudoku and brought them to The Times of London, which began publishing them daily as Times Number Place puzzles. From there they spread across the globe and the UK, and from there, Japan to the US and the rest of the world. Sudoku ( ) literally means single number in Japanese.

What Are The Rules Of Sudoku?

The rules of Sudoku are simple. A Sudoku grid consists of 9 rows of 9 columns with 9 non-overlapping, square 3×3 subgrids. The objective is to fill columns so that each number from 1 to 9 appears exactly once in each column and exactly once in each row. Furthermore, each number from 1 to 9 appears exactly once in each 3×3 subgrid. Here are the complete rules of Sudoku according to the World Puzzle Championship.

  1. Each column of the sudoku puzzle must have the numbers 1-9 with no number repeating.
  2. Each row in the sudoku puzzle must also have the numbers 1-9 without any repetition.
  3. Within each 3×3 box inside the sudoku puzzle, the numbers 1-9 must also appear with no number repeating in any specific column or row.

What Are The Benefits Of Playing Sudoku?

The benefits of playing sudoku include increased cognitive abilities and a sense of well-being.

A study by Franco et al. (2016) published in the Journal of Clinical and Experimental Neuropsychology found that adults who frequently played sudoku had less decline in cognitive function as they aged.

According to Diana Davie of the Alzheimer’s Prevention and Resource Center, exercises such as sudoku and other puzzles are as vital as keeping up with one’s regular exercise program in maintaining a healthy brain.

Improves Concentration

Concentration is the ability to involve the mind in any single activity or task. It is the state of being mentally focused on an idea, activity, or task until its completion. Concentration can be developed by playing sudoku on a regular basis because it is a good brain exercise. As per an article by Electronics & Telecommunications Professor Laurent Miclet at the University of Paris, there is a positive effect of sudoku on the brain’s development associated with the development of concentration.

Enhances Memory

Memory is the ability of a person or another system to store and recall information. According to the Medical News Today article by Jamie Eske entitled Memory Loss: Causes, types, risk factors, diagnosis, treatment (2021), the three fundamental stages of memory are as follows:

  1. Encoding (getting information): Input of information into the brain.
  2. Storage (retaining information): Maintenance of information.
  3. Recall (remembering information): Accessing information stored.

Memory loss, in particular short-term memory loss, is described as the inability to remember past events or recall prior experiences involving one’s memory. Arunas Danusas at Vilnius Gediminas Technical University’s Faculty of Creative Industries published a 2019 article in MDPI where he reports that regularly working with sudoku exercises can help enhance memory, reduce its loss, and slow down its degeneration. Activities such as sudoku which stimulate the utilization of neurological pathways permit messages on sensory receptor nerves to travel the pathways.

Important things that should be remembered are encoded and stored in the brain when various areas of the brain are involved in sudoku. Arunas states that activation has a higher degree during sudoku solving process which helps to keep memories in the brain. Sudoku can be used daily to get memory benefits. A lower efficiency of memory impairment can be achieved by giving 15 minutes per day and then increasing the time available the better one’s sudoku skill becomes.

Relieves Stress

Workplace boredom arises due to mundane work coupled with a lack of control or challenging activity. Sudoku can ease workplace stress by improving focus and relaxation when a break from the primary work is needed.

A study conducted at the Memory and Aging Center at the University of California suggests that long-term engagement with cognitive exercises like sudoku or video games can support healthy financial decision-making, which helps to increase the quality of life and lowers stress.

This stress-relieving Sudoku play puts the human brain through a series of logical procedures, and during stress the play can have the benefit of focusing the mind on reality instead of creative worrying for the user, concurrent with the University of Michigan.

According to science of stress and stress management (Gellert and Gundolf 2018), sudoku and other brain games will enhance the brain’s energy utilization, assist in learning new skills, and even improve complex decision-making and problem-solving skills. Thus, refining the brain is ideal for moving away from the stress of daily life.

How To Fill In Sudoku?

You fill in a Sudoku by using the rule that every row, column, and 3×3 square of the puzzle must contain all the numbers from 1 to 9 with no repeats.

To fill in a Sudoku referred to as Patience Number Puzzle in an English manuscript on page 94 of the October 15, 1897, issue of Collier’s Weekly, one must remember the answer to the basic question of Sudoku. That is, how many numbers are there in a Sudoku game? The answer is that there are 81 spaces. Proceed by trying to solve the easiest numbers, then another basic number, and so on until the entire puzzle is solved. And never forget that tranquility and patience are needed on the road to perfecting such games.

Here is the best approach to pick the right numbers to fill in a Sudoku according to a guide from Angus Johnson of Project Nayuki:

  1. Identify all elements of an empty 3×3 region besides one already (cross out digits already taken in the region). Begin filling in those, updating the elements and region as you make progress. Direct the silhouettes of the digits so that the result created always points to a candidate in that region of 3×3.
  2. If there are no candidate regions for a new number between 1 and 9 in a 3×3 region, update the 3×3 region to work with the next one containing a missing number.

Start With The Easy Puzzles

Starting with the easy rather than hard puzzles is step one of Sudoku instruction. When first learning how to play Sudoku, one must start at a low-difficulty level until they get more comfortable with the game. There are a few tips one must learn when beginning Sudoku that will help them to choose the proper difficulty level. These tips are as follows:

  1. Do not hesitate if you have to replay previous Sudoku puzzles several times.
  2. Try Mimicking the game or View solution with software.
  3. Get comfortable with the game’s layout before moving to a higher difficulty level.
  4. Persevere if you make mistakes on your first few Sudoku attempts.

Use The ‘Pencil In’ Technique

The ‘Pencil In’ technique is part of the terminology of exercising logic in a game of sudoku. Once a cell reaches a point where it could contain 2+ possible unique values based on the constraints on the cells, this is the time to switch to the pencil marking method. As an intermediate sudoku strategy, this let’s you insert smaller possible values into the cell in various corners of the cell to progress with more focused decision steps.

This technique is very important to solve the more difficult sudoku puzzles as it helps the player visualize the possible candidates for an empty cell’s value. In other words, the pencil in method is for when you are not sure of the only possible value that can go in an empty cell, instead you put possibilities which makes it easier to deduce.

Look For Patterns

Sudoku expert suggests that even after you have identified your initial solution in step two, it is worth considering if there are alternate solutions. If there are, you can construct different puzzles using the same initial cell value.

Proving minimality means it is a Sudoku puzzle with only one correct solution according to the World Puzzle Federation.

Professor Sirakoulis, a Greek academic in the Department of Electrical and Computer Engineering of Democritus University of Thrace, alongside his French colleague Professor Regnier, devised a unique solving algorithm named Tarxan. This program constructs new puzzle solutions on its own, making use of both deterministic creativity and evolution of new ideas.

Use The ‘Process Of Elimination’ Method

Use the ‘Process of Elimination’ method to fill in Sudoku by comparing the numbers that appear in a 3 x 3 funny region (fr) at a time and eliminate numbers that can’t be present in the empty cells in this region.

Because when you place a number in a cell, that number in the same row or column (or in box 9 x 9) can no longer be the same number, this is the most important situation that you should take into account when solving the game. To solve the game, you should adapt the possibilities of playing open to the filled with changing formats to advance in the game.

This was mentioned earlier, but this includes the conditions for entering it in the horizontal or vertical line. Note that if you have a solution for a line or column, you need to check if it is overlapping with a solution for another row or column. If they overlap, they help eliminate other numbers in the current row or column. Completing a line or column by using overlapping numbers of another entry can be very beneficial in the game completion.

What Are The Common Mistakes When Filling In Sudoku?

  • Using pen: If playing online, it is hard to change your filled numbers, test with pencil first.
  • Losing focus: Sudoku requires constant focusing or else it often leads to errors.
  • Ignoring cutting edge underscanning and overscanning. The two keys to filling in Sudoku are scanning underscanning and overscanning of neighboring rows and lines for elimination possibilities.
  • Using showing option too early: Using hints only when putting in the next number is difficult.
  • Taking too long to put in the possibility letters: When breaking into a new possibility chain, always check and fill in some majorly easy to spot numbers to make it less of a headache to undo and retrace steps if you make a mistake.
  • Taking too long each turn: The more difficult to find the number, the more time one should allow themselves to quickly revaluate other quick scans to see if they missed an easy fill in.
  • Ignoring the Two-Pattern Rule: Always keep an eye out for when a completed cell did not help and keep an eye out for when there is one single cell with two possible options left.
  • Ignoring the hidden double: Always do a double-check when you find one hidden double, as there could be another hidden double as well. If this results in three numbers, or more in one area, cross-check with any other blank area nearby to guarantee you found a mistake, if not that time spent was wasted.

Repeating Numbers In A Row, Column, Or Box

Repeating numbers in a row, column, or box is not allowed in sudoku. If you realize you have repeated a number, it must be fixed because the puzzle will not be solvable if the grid is in a repeated state. Look at the Medium 1 level of unsolvable puzzles in the inappropriate puzzle section to see an example of this. A full sudoku puzzle cannot have a repeating number in the row, column, or box. Because of the grid structure of sudoku and the fact that it should have only one valid solution, repeating numbers are prohibitive to a valid puzzle and must be resolved.

Not Using The ‘Pencil In’ Technique

  • Definition: Not using the ‘pencil in’ technique means playing the sudoku puzzle in your head without writing potential solutions into open squares (you’re only allowed to use pen anyway).
  • Difficulty: Beginners who wonder how to do difficult sudoku puzzles will deserve an asterisk because doing hard puzzles without some superior logic is nearly impossible without the pencil in approach.

If you are struggling to solve a sudoku puzzle, try following this strategy.

Filling In Numbers Without Logical Reasoning

There are portions of sudoku puzzles that, after one or two logical steps, do not contain other definitive clues, leaving that portion of the puzzle wide open for guesses. In these cases, players must provide an educated guess and manually verify whether the solution is correct.

Different websites with sudoku editors have varying tools to check these unverified locations. Memory-Improvement-Tips suodku software, for example, color-codes incorrect pencil marks that have been entered. These unverified squares can be left blank to await some other part of the puzzle which provides a definitive answer, or guesses can be made in these squares and the sudoku puzzle finished up to quickly verify whether the solutions are correct or not.

How To Solve Difficult Sudoku Puzzles?

Sudoku with an average difficulty level is defined as difficult Sudoku puzzles with about 178 out of 2.0 million givens. These can be solved, for learning how to solve difficult Sudoku puzzles begin solving easy puzzles and figure out the most advanced moves possible. Then move on to solving Chokochoko’s moderate-rated puzzles, where you will find various advanced techniques useful.

Remember to use advanced techniques such as pointing pairs and then box line reduction with hidden pairs in box row as well. Finish by noting all possible moves in a particular cell. For the last possible move, fill it and then complete the puzzle. Finally come to difficult Sudoku puzzles as your skills continue to increase until you can solve these without notes or assists in under five minutes. Remember to watch for the following Sudoku inference properties which are critical knowledge for solving even very difficult puzzles:

    Check out tips for mastering Sudoku.

  • Pointing pair
  • Box-line reduction technique
  • Structure-based exclusion technique
  • Hidden pairs (and other hidden exclusion or constraint property)
  • Constraint-staircase
  • Restricted common

The key to solving truly difficult Sudoku is practice! Repeatedly attempting some single Sudoku levels can help see the patterns that reoccur in different puzzles and understand the algorithmic shortcuts to coming to the end of the puzzle without that much strain.

Use Advanced Techniques

Using Advanced Techniques is the final step of solving sudoku. These advanced techniques are used when you have filled in as many numbers as possible without guessing and the puzzle is still unsolved. Mastering these techniques is not required to solve sudoku, but it can help with the most challenging close-to-unsolvable puzzles. Here is a guide on some of the advanced sudoku strategies, and XY-Wing is one of them XY-Wing: If three cells in a row, column, or box share three possible numbers, you can assume one of those numbers as accurate and use it to eliminate possibilities in other cells.

Practice Consistently

Consistently practicing means finding a regular time and sudoku environment to diligently practice each day. Consistent practice does not mean just sitting there and staring at a particular puzzle for hours. This approach does not help build the foundation of how solvers reach the solution. Consistently practicing solving time-limited puzzles does take daily time and repetitions.

Practice between 30 minutes to a few hours each day. It is better to understand how you got each square on easy or medium puzzles perfectly. The average numbers of squares that experts get correct when starting are low, but they rise as they improve. It is good to strive for perfection on easy puzzles as early as you can. For mastering sudoku: a guide to using notes in solving puzzles, consistent practice is key.

Back off the difficulty until you get a perfect score. This is especially important in the beginning. Ongoing consistent practice to take your time for harder puzzles is also important. The goal is not to get it done with as fast as possible. The goal is to get better. Striving for excellence is what leads to success, rather than just having the finishing the puzzle itself as the goal.

Try Different Strategies

Try different strategies for solving Sudoku and choose the one that works best for you. Even if you already know your optimal fill-in-the-blank strategy, it is wise to regularly try a few others so that you can notice if there is a new best strategy for you as your skill level improves.

One common strategy is the Simple Coloring technique. This can sometimes help to easily and accurately fill in numbers when they are hidden in hard-to-find spots. The image in the figure below illustrates the simple coloring technique. The blue path creates a link between the red number 3 on the right and the red number 1 on the left. Heaney calls this “True Nice Loop, Type 1”.

Other common solving techniques include X-Wing, Su-Box, XY-Wing, XYZ-Wing, Jelly Fish, Kite, Windoku, and many more. These methods can involve imaginative or even absurd interpretations of where Almost Complete Sets are, so do not be afraid to use what works for your problem if the non-logical steps proposed in those strategies do not always make sense.

In the video, Simon Anthony briefly presents some advanced solving strategies which are covered in more detail by Cracking The Cryptic,, and the Andrew Stuart sudoku techniques glossary.

What Are The Strategies For Solving Different Types Of Sudoku Puzzles?

These are the key strategies for solving different types of sudoku puzzles:

  1. Standard sudoku puzzles: Use elimination and assignment to logically fill in spaces
  2. Odd-even and higher-lower sudoku: Look for toggle cells with one of two numbers that will help introduce a ‘low’ or ‘high’ set of numbers
  3. Hyper sudoku puzzles: Using two sets of numbers, solve each 3×3 block individually
  4. Diagonal sudoku puzzles: Focus on the diagonals
  5. Letter sudoku puzzles: Look for words or unusual fill numbers to jump-start the puzzle

Classic Sudoku

The classic Sudoku puzzle is the most common variant and appears in newspapers, websites, and books around the world. A classic Sudoku puzzle has 9 rows, 9 columns, and 9 blocks. It will only contain three numbers per line and repeat these four times. The rules of Sudoku are simple. Fill in the grid so that every column, row, and block contains all the numbers from 1 to 9 once each.

Killer Sudoku

The solution process for Killer Sudoku is the same as for standard sudoku. First, look for squares with the fewest possibilities and try to assign values to them. If you get stuck or need to check, use inverse sudoku. Calculator techniques can be useful in the rare situations when there are not enough given numbers.

Fill in Killer Sudoku as you would normal sudoku. But in addition to assigning the number (1-9) the goal of Killer Sudoku is to let the reader know which groups of squares containing any number of squares (not just lines) combine via a sum rule together. Represent the sum of multiple blocks with a + symbol as shown in the Killer Sudoku grid. The sum of these blocks must equal the sum provided at the beginning of the line.

Samurai Sudoku

Samurai Sudoku is a more advanced version that consists of five smaller (mini) Sudoku puzzles on the same grid. It was introduced by Nikoli to the Times. Each mini Sudoku puzzle has less area as a regular Sudoku, so Samurai Sudoku has an extra higher level of difficulty. The rule is that every 3×3 region can only have unique numbers. This makes for another challenging daily puzzle, as you must employ more advanced sudoku strategies to progress.

Frequently Asked Questions

How to Fill in Sudoku?

Question: What is Sudoku? Sudoku is a popular logic-based number placement puzzle game.

How to Fill in Sudoku?

Question: How do I play Sudoku? The objective of Sudoku is to fill a 9×9 grid with numbers so that each row, column, and 3×3 subgrid contains all the numbers from 1 to 9.

How to Fill in Sudoku?

Question: What are the rules of Sudoku? The rules of Sudoku are simple – each row, column, and 3×3 subgrid must contain each number from 1 to 9 without any repeats.

How to Fill in Sudoku?

Question: How do I start filling in a Sudoku puzzle? Start by looking for numbers that are already given in the puzzle, and then use logic and deduction to fill in the remaining empty spaces.

How to Fill in Sudoku?

Question: What strategies can I use to fill in Sudoku puzzles? Some common strategies for filling in Sudoku puzzles include scanning, marking up possible options, and using the process of elimination.

How to Fill in Sudoku?

Question: Is there a specific order to fill in the numbers in a Sudoku puzzle? No, there is not a specific order to fill in the numbers in a Sudoku puzzle. You can start with any number and fill in the remaining spaces accordingly.

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