JavaScript step-by-step Sudoku solver and board generator
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README.md

#SudokuJS ##JavaScript Sudoku solver

Live demo on: https://jonassebastianohlsson.com/sudoku/

SudokuJS has a step by step solver that implements basic strategies, enough to solve (non evil) newspaper sudoku puzzles. The solver is built to mimic humans in that it attempts strategies in order from easiest to most difficult, in each step. So if you're stuck with a puzzle this solver will show you the minimal next step to continue.

SudokuJS comes with a basic GUI for the sudoku board - the board is rendered on the screen, and the board cells listen for keyboard input from a user.

SudokuJS can generate sudoku puzzles of the same difficulties that it can solve, ranging from Easy to Very hard.

SudokuJS currently requires jQuery (on TODO to remove this dependency).

Usage

Initialization

<script src='sudokuJS.js'></script>
<link rel='stylesheet' href='sudokuJS.css' />

<div id='sudoku'></div>

<script>

var mySudokuJS = $("#sudoku").sudokuJS({
    difficulty: "medium" ("easy"|"medium"|"hard"|"very hard")
});
</script>

You can also pass in your own board:

//array representing a standard sudoku puzzle of size 9
//use space for empty cells
var board = [
	, , ,4, ,8, ,2,9
	, , , , , , , , ,4
	,8,5, , ,2, , , ,7
	, , ,8,3,7,4,2, ,
	, ,2, , , , , , ,
	, , ,3,2,6,1,7, ,
	, , , , ,9,3,6,1,2
	,2, , , , , ,4, ,3
	,1,3, ,6,4,2, ,7,undefined
]
//NOTE: if last cell of board is empty, 'undefined' has to be used as value!
var mySudokuJS = $("#sudoku").sudokuJS({
		board: board
});

Solving

Let SudokuJS solve your puzzle - either step by step, or all in one go:

mySudokuJS.solveStep();
mySudokuJS.solveAll();

Analyzing the board

The solver can tell you info about the board.

var data = mySudokuJS.analyzeBoard();

//data.error -- board is incorrect
//data.finished === false -- board can't be solved because it requires more advanced strategies

//if no error, and data.finished === true
//data.level -- "easy"|"medium"|"hard"
//data.score -- int [experimental]
//data.usedStrategies -- [{title, freq}, ..],ranked by difficulty, easiest first

Board Generation

SudokuJS generate new sudoku puzzles on init when no board is passed in, and on generateBoard calls:

mySudokuJS.generateBoard('easy');
mySudokuJS.generateBoard('medium');
mySudokuJS.generateBoard('hard');
mySudokuJS.generateBoard('very hard');

The current implementation for board generation cannot guarantee hard or very hard puzzles generated on every try, so instead it continues over and over until is has succeeded. This means loading a very hard board can sometimes take up to a few seconds.

generateBoard accepts a callback function as a second paramater, that gets called when the new board is ready.

Candidates

Candidates are hidden when a board loads. To show/hide candidates:

mySudokuJS.showCandidates();
mySudokuJS.hideCandidates();

SudokuJS automatically removes impossible candidates on showCandidates(); candidates that can be eliminated via visualElimination (number already exists in same house).

Candidates can be edited on the board by setting SudokuJS to candidate editing mode:

mySudokuJS.setEditingCandidates(true);

Input changes on board cells will now toggle the candidates rather than changes the value.

Clear board

Useful before entering new puzzle, if using keyboard input in the GUI.

mySudokuJS.clearBoard();

Get/Set board

Get the board and save it away if you want. Set a new board and play with that one instead. Setting automatically resets everything back to init state.

mySudokuJS.getBoard();

var newBoard = [
	...
]

mySudokuJS.setBoard(newBoard);

Callbacks

boardUpdatedFn

Fires whenever the board is updated, whether by user or solver.

 $("#sudoku").sudokuJS({
	board: board
	,boardUpdatedFn: function(data){
		//data.cause: "user input" | name of strategy used
		//data.cellsUpdated: [] of indexes for cells updated
		alert("board was updated!");
	}
});

boardFinishedFn

Fires when the board has been completed.

 $("#sudoku").sudokuJS({
	board: board
	,boardFinishedFn: function(data){
		//ONLY IF board was solved by solver:
		//data.difficultyInfo {
		//	level: "easy", "medium", "hard"
		//	,score: int [experimental]
		//}
		alert("board was finished!");
	}
});

boardErrorFn

Fires whenever the board is found to be incorrect, f.e. if solver detects there is no solution to board, or if passed in board is of invalid size.

 $("#sudoku").sudokuJS({
	board: board
	,boardErrorFn: function(data){
		//data.msg -- f.e. "board incorrect"
		alert("board error!");
	}
});

candidateShowToggleFn

The solver automatically switches to showing candidates when a solve step was invoked which only updated the candidates on the board. To catch this change (for updating UI, etc), there is a callback:

 $("#sudoku").sudokuJS({
	board: board
	,candidateShowToggleFn: function(showingBoolean){
		alert("candidates showing: " + showingBoolean); //true|false
	}
}

Extra

The solver is board size agnostic, so you can pass in any valid sudoku sized board (f.e. 4x4, 9x9, 16x16) - however the CSS included only handles 9x9 boards. Currently you can't change boardSize after init.

License

MIT

Changelog

0.4.5 boardSize option, now working. Demos for board sizes 0.4.0 Candidate editing mode
0.3.0 Board generator, easy - very hard
0.2.0 Simple UI and better interface
0.1.0 Step by step sudoku solver