Levels

When we talk about levels we refer to the difficulty to solve a sudoku game. Among sudoku lovers we will find from beginners to expert scholars. This explains why all publications and applications disclose the level of difficulty, so that each player can choose the level they want to play at.

Diffulty to solve Sudoku Games

Although it is not trivial to determine how difficult it is to solve a game, at CrossGames21 we simplify this by associating difficulty with the number of steps required to reach the final solution.

Steps to Solve

What does it mean how many steps do I need to solve a game ? We determine the number of steps as follows : For all the cells we write down all the possibilities of numbers that can be placed in them. In the first step, we fill with your number those that have only one option. Once the first step has been executed, options are discarded in the remaining cells. In the second step, all the numbers that are now unique options are placed. After the second step is executed, new option discards occur in the remaining cells, which leads to the third step, and so on.

Let’s see a first example of an easy Sudoku to solve. This game has 53 visible cells, and is solved in just 2 steps. In the first step, there are 20 cells with a single option. Once these 20 numbers have been placed, the remaining 8 cells also have a single option to solve in the second step.

Let’s see a second example of Sudoku more difficult to solve, a game with 30 visible cells. As you can see, this game requires 4 steps to solve.

Steps vs Visible Cells

In summary, by solving many games with different numbers of visible cells, we were able to build this graph that suggests the level of difficulty according to the necessary steps, which depend on the number of initial visible cells.

Levels in CrossGames21

According to what we have explained in this article, in CrossGames21 we define the different levels of difficulty according to the following table

Level	Visible Cells	Hidden Cells	Steps to Solve (aprox)	%Cells solved in 1st Step
Extreme19	19	62	12	8%
Challenge21	20-21	60-61	9-11	10%
Daily	21	60	9	12%
Advanced Plus	22-25	56-59	7	13%
Advanced	26-30	51-55	5	20%
Classic Plus	31-35	46-50	4	42%
Classic	36-41	40-45	3	63%
Beginners Plus	42-48	33-39	2	84%
Beginers	49-55	26-32	1-2	90%

Other topics

CrossGames21	Presentation
The Sudoku Game	Explanation of the sudoku game
Games	Explanation of all games in CrossGames21.com
Levels	Difficulty levels of the games
Rules	Use of options / board and keyboard in CrossGames21.com
Techniques	Tricks to solve sudoku games
Statistics	Statistics of games in CrossGames21.com