Sudoku.jl provides the following methods for solving and displaying sudoku puzzles:

Constructing sudoku puzzles

sudoku

Create a SudokuPuzzle from a string, for example:

julia> sudoku("003020600900305001001806400008102900700000008006708200002609500800203009005010300")
    3|  2  |6
9    |3   5|    1
    1|8   6|4
-----+-----+-----
    8|1   2|9
7    |     |    8
    6|7   8|2
-----+-----+-----
    2|6   9|5
8    |2   3|    9
    5|  1  |3

1  sudoku(init::AbstractString)

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from_file

Parse a file into a list of strings, separated by sep.

1  from_file(filename)
2  from_file(filename, sep)

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show

Display puzzles as a 2-D grid.

1  show(io::IO, grid::Sudoku.SudokuPartial)
2  show(io::IO, p::Sudoku.SudokuPuzzle)

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Solving puzzles

propagate

Convert grid to a SudokuPartial of possible values, vals is a BitArray{2} remove values already seen in a shared unit

Returns false if a contradiction is detected.

1  propagate(grid::Sudoku.SudokuPuzzle)
2  propagate(grid::AbstractString)

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solve

Solve a sudoku puzzle.

1  solve(p::Sudoku.SudokuPuzzle)
2  solve(init::AbstractString)

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solve_all

Attempt to solve a sequence of grids. Report results.

Display the puzzles that take longer than showif seconds to solve, see time_solve.

1  solve_all(grids)

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is_solved

Returns true if the grid is completely filled in.

1  is_solved(grid::Sudoku.SudokuPartial)

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Creating random puzzles and testing performance

random_sudoku

Make a random puzzle with N or more assignments. Restart on contradictions.

Note the resulting puzzle is not guaranteed to be solvable, but empirically about 99.8% of them are solvable. Some have multiple solutions.

1  random_sudoku()
2  random_sudoku(N::Integer)

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time_solve

Time how long it takes to solve grid.

If it takes longer than showif seconds to solve, print grid and whether or not it has been solved.

This is useful for finding "difficult" random puzzles.

1  time_solve(grid, showif)

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bench

Benchmarking: Solve some some example puzzles:

  • easy (from easy.txt)
  • hard (from top95.txt)
  • hardest (from hardest.txt)
  • 100 random puzzles.
1  bench()
2  bench(N::Integer)

Source: 1 2.

Internal

Internally the following functions do the searching and propogation:

Using depth-first search and propogation, try all possible values.

1  search!(vals::BitArray{2})

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eliminate!

Eliminate d from vals[:, s]; propagate when values or places <= 2. Returns false if a contradiction is detected.

1  eliminate!(vals::BitArray{2}, s::Int64, d::Int64)

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assign!

Eliminate all the other values (except d) from vals[:, s] and propagate.

Returns values, or false if a contradiction is detected.

1  assign!(vals::BitArray{2}, s::Int64, d::Int64)

Source: 1.