Sudoku solver in JS

Question

I'm trying to write an algorithm that can solve sudoku. For now, my code works till supplyGrid is out of numbers. When it happens it should go back and try another number, right? To be honest I have no clue how to achive that.

var grid = [
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, 0]
],
    supplyGrid = [1, 2, 3, 4, 5, 6, 7, 8, 9],
    row = 0,
    col = 0,
    value = 0,
    index = 0;


var solveSudoku = function (grid, row, col) {
    if (col > 8) {
        row++;
        col = 0;
        if (row > 8 && col > 8) {
            console.log(grid);
            return;
        }
    }
    if (grid[row][col] === 0) { //
        index = Math.floor(Math.random() * supplyGrid.length);
        value = supplyGrid[index];
        if (isValid(row, col, value)) {
            grid[row][col] = value;
            col++;
            supplyGrid = [1, 2, 3, 4, 5, 6, 7, 8, 9];
            solveSudoku(grid, row, col);
        } else {
            supplyGrid.splice(index, 1);
            console.log(supplyGrid);
            if (supplyGrid.length < 1) { 
                //backtrack();
                console.log('Out of numbers');
                return;
            }
            solveSudoku(grid, row, col);
        }
    } else { //row = 3, col = 5
        solveSudoku(grid, row, ++col);
    }
    return this;
}

function isValid(row, col, value) {
    if ((validateColumn(row, col, value)) || (validateRow(row, col, value)) || (validateBox(row, col, value))) {
        return false;
    } else {
        return true;
    }
}

function validateBox(row, col, value) {
    row = Math.floor(row / 3) * 3;
    col = Math.floor(col / 3) * 3;
    var isFound = false;
    for (var i = 0; i < 3; i++) {
        for (var j = 0; j < 3; j++) {
            if (grid[row + i][col + j] == value) isFound = true;
        }
    }
    return isFound;
}

function validateRow(row, col, value) { 
    var isFound = false;
    for (var i = 0; i < 9; i++) {
        if (grid[row][i] === value) isFound = true;
    }
    return isFound;
}

function validateColumn(row, col, value) { 
    var isFound = false;
    for (var i = 0; i < 9; i++) {
        if (grid[i][col] === value) isFound = true;
    }
    return isFound;
}

Answer 1

I solved this question with backtracking algorithm:

const _board = [
    ['.', '9', '.', '.', '4', '2', '1', '3', '6'],
    ['.', '.', '.', '9', '6', '.', '4', '8', '5'],
    ['.', '.', '.', '5', '8', '1', '.', '.', '.'],
    ['.', '.', '4', '.', '.', '.', '.', '.', '.'],
    ['5', '1', '7', '2', '.', '.', '9', '.', '.'],
    ['6', '.', '2', '.', '.', '.', '3', '7', '.'],
    ['1', '.', '.', '8', '.', '4', '.', '2', '.'],
    ['7', '.', '6', '.', '.', '.', '8', '1', '.'],
    ['3', '.', '.', '.', '9', '.', '.', '.', '.'],
];
sodokoSolver(_board);
console.log(_board);

function isValid(board, row, col, k) {
    for (let i = 0; i < 9; i++) {
        const m = 3 * Math.floor(row / 3) + Math.floor(i / 3);
        const n = 3 * Math.floor(col / 3) + i % 3;
        if (board[row][i] == k || board[i][col] == k || board[m][n] == k) {
          return false;
        }
    }
    return true;
}


function sodokoSolver(data) {
  for (let i = 0; i < 9; i++) {
    for (let j = 0; j < 9; j++) {
      if (data[i][j] == '.') {
        for (let k = 1; k <= 9; k++) {
          if (isValid(data, i, j, k)) {
            data[i][j] = `${k}`;
          if (sodokoSolver(data)) {
           return true;
          } else {
           data[i][j] = '.';
          }
         }
       }
       return false;
     }
   }
 }
 return true;
}

Answer 2

Here is an open source repository which has provided a javascript solution:

https://github.com/pocketjoso/sudokuJS

Here is the code which details his solution:

https://github.com/pocketjoso/sudokuJS/blob/master/sudokuJS.js