The Tricks of Sudoku Solver Algorithm Java

By now just about everyone has seen the Java sudoku solver algorithm that’s made the rounds across the Internet. Plenty of people have already seen the source code, but they might be curious as to how it works. The majority of the methods seen require input to the solution from the command line. Perhaps the most innovative way of doing this was to input each individual row of the problem as a string and show the whole sudoku board as an array.

10 Tricks to Sudoku Solver Algorithm Java

So now that you have understood the basic concept of how the Sudoku solver algorithm java works, what are some tricks you can use to better your skills at it? Well, we have compiled a set of suitable tricks that enable you to achieve core techniques and get results much quicker.

These include:

1.Understanding the Sudoku puzzle on a deeper level 

Yep, a lot of people know what Sudoku is. But have they really taken the time to understand what the game is all about? In fact, the first step to knowing Sudoku like the back of your hand is to understand the rules.
They are pretty straightforward and consist of the following set features:

  • There is a board that consists of a 9×9 matrix, which is then subdivided into various sub-sections (9 in total)
  • Each square can have a possibility of a number from 1 to 9
  • Each of the numbers in a row must be unique
  • Each number in a column must be unique as well
  • Each number in each section must be unique

2. Knowing the mechanics of the game

Even though the rules might look easy peezy, the mechanics of how the game can work varies depending from one game to another.

In fact, there are some variations such as:

  • There are game boards that are played concurrently while others are played once at a time
  • Some game boards validate the inserted number after every turn while others validate the all the numbers after you have completed your number sorting and selection.
  • In some Sudoku puzzles, they use more than numbers. They can even use certain numbers of the alphabet during gameplay.

3. Knowing how to read the pattern of Sudoku

As you know, the Sudoku puzzle can be a complex little nightmare that can render you to quite some sleepless nights if not properly addressed. So there’s the whole pattern situation that needs to be looking out for especially when writing code. Of course, you can use the java solver to make things easier for you. But to do so, you need to have the java rules and memorize them by heart.

4. Repeating the validation

Doing the validation of specific cells means that you will have to look and find out whether the number you have inserted will be present in the 8 other values of that row, as well as the 8 other values of that column; not to forget the entire section! So supposes it’s a 9x9x9 matrix that would mean you would have to do 1944 tests! See the importance of the solver now?

5. Address the issue of missing numbers

At some point or another; you must have figured out that using the solver isn’t a matter of just fitting numbers here and there; but rather determining what fits on the entire board. That being said, here’s where things get a little tricky; you can be left with cells that do not have any suitable numbers! But don’t panic, here’s where you can introduce three procedures in your code that include…

6. Use the backtracking algorithm

This is an awesome way to solve any errors of the Sudoku problem. Here’s the catch though, it’s a trial and error technique. So you’ve got to plug in a number of possibilities until eureka! Problem solved. Good thing is that you can use Java to do the dirty work of plugging in these possibilities.

7. Looking out for the next empty square

This is practically child’s play. All you need to do is begin from your current square, and move through the matrix to find the next value. Not time conservative, but pretty easy to understand.

8. Locating legal numbers for each cell

Here, you can start by going over each row, column, and segment while checking out the numbers that have already been used. Once done, you will be left with some particular elements, which you can then use in the given cell missing a certain number. Great right!

9. Making the solver much faster

By now, you’re pretty aware of how to shorten long texts of code using simple techniques. Well, the shorter the code obviously, the much faster the compiler will work to retrieve your desired answer. SO if possible you can avoid long lines of code, by all means, do so! Just make sure that it is right and executes the job accurately. Your aim is to find the least path of resistance!

10. Don’t bust a brain nerve

It’s critical that you don’t let the complexities of the Sudoku solving get to you. In fact, have fun at solving it with Java while you are at it. Remember, creativity is all you require in code writing, and figuring out how the system works. If it’s not fun, then it’s not part of the spirit of Sudoku which is a leisure activity!

Solving a Sudoku Puzzle

sudoku solver algorithm javaThose who are working on writing Java sudoku solver might want to have a look at an eight queens puzzle or some other similar one. All of these backtracking puzzles use some form of the same source code, which helps when it comes time to solve the problem.

Even those without experience should be able to understand the way the Java source code parses input though:

public static void main(String[] args) {

int[][] array = parse Problem(args);


if (solve(0,0,array))


Here the Java sudoku solver algorithm takes what the user writes on the command line and places it into arrays for use later. The actual solving workplaces the data taken from arrays and sending it through a series of loops that ensure that each row, not a box, includes every number from 1-9 only once. This is sort of the trick considering that the program looks at a sudoku problem a little differently from most human solvers.

Each loop would then print the numbers across in rows as follows:

static boolean solve(int i, int j, int[][] boxes) {

if (i == 9) {

i = 0;

if (++j == 9)

return true;


if (boxes[i][j] != 0)

return solve(i+1,j,boxes);

sudoku solver algorithm java tricks

Sudoku Source Code

sudoku solver java source codeNote that the actual Java source code checks to make sure that each box is unfilled, and skips filling it in. By the time all these loops run everything has been filled. These are the sorts of quick little programming tricks professionals can add to make an applet work right the first time.

Still not getting the sudoku solver algorithm java thing? Ask out our team for some help!