Credit: Hans-Peter Gauster - Unsplash What is a genetic algorithm? Principle Here is why we can try another approach by using a genetic algorithm. That is, the time required to solve the problem using any currently known algorithm increases rapidly as the size of the problem grows” 6. Note: “if a solution to an NP-complete problem can be verified quickly, there is no known way to find a solution quickly. With greater size, it is not so easy and even for some 9x9 puzzles, sometimes it is difficult to solve them ‘just with logic’ and you need to bet on some answers to move on. Solving NxN Sudoku puzzles is known to be NP-complete. Pencil mark can help to fill some cells but it might stop because at some point there is no more cell with single value to safely assign. Using backtracking works fine for small grid sizes but becomes computationally unaffordable for larger grid sizes. For easy puzzles, this solution is sufficient to solve them. Then we start again until there is no more cell with unique value to assign. Some cells will have only one possible value so it is safe to assign this Pencil mark approach consists in filling all cells with possible values (i.e a value is which not already present in same row/column/grid) 5. If one of its advantages it to guarantee a solution will be found, a major drawback is that solving time may be slow due to the solutions tree sequential exploration. Principle is to fill empty cells with a value that satisfies the constraints, moving forward to the next cell when it works, moving backward when there is a constraint violation. That would take ages to run.īacktracking is also a kind of brute force search. Of course basic brute force is not an option: for a 9x9 grid puzzle, “number of essentially different solutions, when symmetries such as rotation, reflection, permutation, and relabelling are taken into account, was shown to be just 5,472,730,538“ 4. With a 9x9 puzzle, you should be able to solve the sudoku with another approach than deploying a genetic algorithm: Backtracking 1 2, Operations Research (as it is a Constraint Satisfaction Problem 3), Pencil Mark.Īnd I am pretty sure that a lof of others exists if you have time for a little googling session. Solving sudokus with computer: a lot of approaches are available Objective was also to improve my personal skills in Python but perhaps sometimes my choices/approaches are not so 'pythonic', sorry about that.I could have used some libs such as pyevolve but the goal was more to understand how Genetic Algorithms works, what I am doing and why I am doing it.This project is only for personal challenge and educational purpose, no other pretention than those ones.

Right angles give you a lot of information regarding the empty columns and rows in the cell they’re in, which can help you cancel out incorrect candidates in the adjacent cells. Right angles (any 3 given numbers in an L-shape inside of a cell).This pattern can help you isolate rows and columns to solve entire rows or columns of the puzzle. Skyscrapers (two rows or columns of a given candidate that are unequal in length).Revisit these regularly to make sure you don’t provide a false solution. Corner patterns help eliminate a ton of potential candidates in the rows and columns connected to it. Corners (a collection of 4 solved squares in any of the 4 corners).X Research source A few common patterns include: There are a bunch of different patterns out there, but if you can spot one, they’ll typically help you solve some element of the puzzle that you’re struggling with. Patterns refer to configurations of solved squares that help players regularly solve a sequence of candidates. There are a handful of patterns most players look for at this point.

Pseudocode for solving sudoku