Published on rubygems here: https://rubygems.org/gems/sudokude

Sudokude solves Sudoku puzzles for you! It's a very simple gem, and exposes two methods:

1. It can solve a sudoku puzzle via .solve
2. It can stringify the sudoku puzzle (solved or unsolved) via .to_s

gem install sudokude

1. Initiate an instance of a Sudoku class with Sudokude::Sudoku#new
2. Pass in a matrix (array of arrays) for a sudoku puzzle. Each blank cell should be passed in as nil. The array should consist of 9 sub-arrays, one sub-array for each row in a Sudoku puzzle, in order from top to bottom, and left to right. For example, this sudoku puzzle will look like:

[
  [4,   nil, 9,   1,   3,   7,   nil, nil, nil],
  [nil, nil, nil, 8,   2,   9,   nil, 6,   nil],
  [2,   nil, 7,   nil, nil, nil, nil, 9,   nil],
  [nil, 5,   6,   nil, nil, 8,   nil, nil, 9  ],
  [nil, nil, nil, 3,   5,   1,   nil, nil, 6  ],
  [1,   nil, nil, nil, nil, nil, 8,   5,   nil],
  [nil, nil, nil, nil, 1,   nil, 9,   2,   4  ],
  [6,   2,   nil, 7,   nil, 3,   nil, nil, nil],
  [nil, nil, nil, nil, 8,   2,   6,   7,   3  ]
]

3. Call .sovle on the instance to solve. The gem will either return a solved puzzle, or return an error if the puzzle is not possible to solve