Crate sudokugen

Sudoku puzzle solver and generator library.

Sudokugen can find a solution to a valid puzzle using a mixture of basic strategies and bruteforce. It can also generate new minimal puzzles. This library was built as a rust learning project for myself.

How to use Sudokugen

Sudokugen offers two convenience functions, solve and generate to solve and generate sudoku puzzles and a struct Board to help you inspect and manipulate them.

You can parse a puzzle from a string:

use sudokugen::Board;

let board: Board = "
     . . . | 4 . . | 8 7 .
     4 . 3 | . . . | . . .
     2 . . | . . 3 | . . 9
     ---------------------
     . . 6 | 2 . . | . . 7
     . . . | 9 . 6 | . . .
     3 . 9 | . 8 . | . . .
     ---------------------
     . . . | . . . | . 4 .
     8 7 2 | 5 . . | . . .
     . . . | 7 2 . | 6 . .
".parse().unwrap();

After it's parsed you can solve it using the solve function:

use sudokugen::solve;

assert_eq!(
    solve(&board).unwrap(),
    "695412873413879526287653419146235987728946135359187264561398742872564391934721658"
    .parse()
    .unwrap()
);

Finally you can generate new puzzles using generate, the parameter 3 here indicates that you would like a puzzle of base size 3, which translates to a 9x9 puzzle.

use sudokugen::generate;

let puzzle = generate(3);

println!("Puzzle\n{}", puzzle.board());
println!("Solution\n{}", puzzle.solution());

Which will print something like this:

> Puzzle
> . . . . . . . 6 .
> . 1 7 . 4 . . 9 .
> . . . . 9 . 5 3 .
> . . 5 . 7 2 8 . .
> 1 . . . . 8 4 5 .
> . 4 . 9 . . . . .
> 8 7 9 1 2 . . . .
> 4 5 . 8 . . . . .
> . . . . . . . . .
>
> Solution
> 9 2 3 5 8 1 7 6 4
> 5 1 7 6 4 3 2 9 8
> 6 8 4 2 9 7 5 3 1
> 3 6 5 4 7 2 8 1 9
> 1 9 2 3 6 8 4 5 7
> 7 4 8 9 1 5 6 2 3
> 8 7 9 1 2 6 3 4 5
> 4 5 6 8 3 9 1 7 2
> 2 3 1 7 5 4 9 8 6

Crate Layout

This crate is divided in three modules. board contains the tools needed to parse, manipulate and print a puzzle and it's individual cells. solver contains the solve function and generator contains the generate function as well as an umbrella struct to hold the puzzle and it's solution.

Puzzle quality

Grading puzzles is beyond the scope of this crate. The reason behind it is that grading puzzles correctly, requires solving them like a human would and some of the more complex techniques to solve a puzzle like a human would require a lot of computations that do not always payoff performance-wise.

That being said, the generated puzzles consistently have between 22 and 26 clues making them likely on the harder side of most generally available puzzles.

Is it fast?

The quick answer is, it depends on your use case. The solve function is optimized to be decently fast for a 9x9 sudoku puzzle, in my 2017 MacBook Pro it takes an average of 300μs to solve a difficult puzzle, that is around 3000 puzzles per second.

The generate function is less optimized and makes heavy usage of solve without trying to re-use repeated computations, as such it's much slower clocking at about 18ms to generate a new puzzle in my benchmarks.

You can run your own benchmarks with cargo bench

Re-exports

pub use board::Board;

pub use solver::generator::generate;

pub use solver::solve;

Modules

board	The Board module contains representations of a sudoku Board as well as the representation of a cell location inside a board CellLoc.
solver	Offers a function to help you solve sudoku puzzles. The solve function takes a sudoku puzzle and returns a new board with the solution, if there is one.