sudoku-solver

A simple recursive backtracking algorithm for solving Sudoku puzzles when given a 81 character string.

Features

• Ability to solve a given sudoku string when given as a string argument via 'sudosolve()'
• Ability to solve and save a file of sudokus when given a filename argument via 'sudoparse()'

Important info

How to format an input Sudoku string

To write a Sudoku grid as a valid Sudoku string input, simply type the square values left to right, top to bottom , while writing unknown values as "0", it is important you type the entire grid in quotes so Python recognises it as a string input rather than variable, here is an example grid: "000075400000000008080190000300001060000000034000068170204000603900000020530200000"

How to solve an input string

To solve an input Sudoku string, simply type into the python console sudosolve(sudokustring) Optional arguments include 'report', which is enabled by default and will print a report of the solving process, and 'string_is_list' which is disabled by default, set this argument to true if you wish for sudosolve() to not print a report but still return the time taken alongside the solved grid, e.g if it is part of a wider function. here is an example of how you can solve your string sudosolve("000075400000000008080190000300001060000000034000068170204000603900000020530200000")

How to format an input Sudoku file

The file should contain one properly formatted sudoku string on each line, if spread across multiple lines the program will not work, in the included sample_grid file you can see what a properly formatted Sudoku input file looks like

How to solve an input Sudoku file

With sudosolver.py being ran in the Python console, type sudoparse(filename) Optional arguments include 'outputfile' , if this argument is specified the solved grid will be saved to the outputfile given to it as an argument. Here is an example of how you can solve a sudoku file from sample_grids
sudoparse("sample_grids/sample-25clues.txt")

How to view a solved or unsolved Sudoku

To view the current state of the Sudoku grid, type in the sudosolver.py Python console sudoprint(), this is a simple function that will display the grid in text square form

How it works

This Sudoku solver is made fairly simply using recursive backtracking, so the process of solving a grid essentially looks a little like this

• Check if the grid is already solved, if so return the grid
• Pick the first square that is unknown (contains a 0)
• If no digit can be placed in this square, return to the calling function False
• If digit(s) can be placed in this square, try them in order
• call this function (go back to step 1) and if it returns False set the squares value to 0 again and try the next digit
• if no digit is found that does not return false then return False