An approach to solve sudokus with a genetic algorithm
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Marcel Moosbrugger
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Genetic sudoku solver

GSS is an approach of solving sudokus with a genetic algorithm. The project is more of educational purpose, as Java doesn't allow the most performant implementation, but greatly illustrates the architecture of such an algorithm. Nevertheless GSS solves most sudokus in a decent time. Additionally to standard 9x9-sudokus, the program is able to solve bigger sudokus like e.g 16x16 or 25x25.


You can either clone this repository or download the jar-file by clicking here.


Call the following command in your terminal to start the program.

java -jar genetic-sudoku-solver.jar

After that GSS asks you the side length of a block of the sudoku you want solve. Here you type '3' for a standard sudoku. For bigger sudokus you put e.g. '4' for a 16x16 puzzle or '5' for a 25x25 puzzle.

>> Size of a block ('3' for standard sudoku): 3

Succeeding, GSS requests the sudoku-grid to solve

>> Sudoku ('0' for empty fields):
0 0 0 0 0 0 3 8 0
0 0 0 3 4 6 0 0 0
0 5 1 0 0 0 0 0 0
2 0 0 8 0 3 0 0 6
0 6 0 0 0 0 5 0 9
0 1 5 2 0 0 0 0 0
0 0 0 0 3 0 6 7 0
0 0 2 0 0 0 0 5 0
6 0 4 0 7 2 0 0 0

For a 9x9-sudoku you could alternitavely omit the spaces between the numbers.

>> Sudoku ('0' for empty fields):

As soon as you end your input with the EOF-character the algorithm starts solving your sudoku.


You can tweak the behaviour of the GSS with a few parameters. The parameters get passed to the program on startup.

java -jar genetic-sudoku-solver.jar -e 0.001

This would result in the elitism-rate changed to 0.1 %.

Parameter Default value Name Description
-e 0.002 Rate of elitism Determines how many of the fittest individuals get automatically added to the next generation.
-m 0.1 Rate of mutation The probability of an individual to mutate.
-p 1000 Population size The number of individuals in a single population.
-b 20 Idle generations before restart If after this many generation no progress was made, the algorithm gets restarted.
-n 2 Number of parents The number of individuals (parents) from which a new individual (child) is derived.
-l 0 Number of fields left empty by the presolver This many fields get left empty by the presolving algorithm, albeit it could know the answer.

Technical details


Before the genetic algorithm gets applied, the program uses a simple method to fill in some of the empty fields. More easier puzzles will be solved completely after this step, harder puzzles may even stay the same. If you want to regulate how much of the sudoku-grid is solved or skip the presolving step completely, use the '-l' parameter.


After some number of generations in which no progress was made (can be configured with the '-b' parameter), the genetic algorithm gets restarted. Before each restart the fittest individuals get stored. If enough elites have been stored the restart is done with a population containing all stored elites.


An explanation of genetic algorithms in general can be found on my blog.