script.js

var arr = [[], [], [], [], [], [], [], [], []]
var temp = [[], [], [], [], [], [], [], [], []]

for (var i = 0; i < 9; i++) {
    for (var j = 0; j < 9; j++) {
        arr[i][j] = document.getElementById(i * 9 + j);

    }
}

function initializeTemp(temp) {

    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            temp[i][j] = false;

        }
    }
}


function setTemp(board, temp) {

    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            if (board[i][j] != 0) {
                temp[i][j] = true;
            }

        }
    }
}


function setColor(temp) {

    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            if (temp[i][j] == true) {
                arr[i][j].style.color = "#DC3545";
            }

        }
    }
}

function resetColor() {

    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {

            arr[i][j].style.color = "green";


        }
    }
}

var board = [[], [], [], [], [], [], [], [], []]


let button = document.getElementById('generate-sudoku')
let solve = document.getElementById('solve')

console.log(arr)
function changeBoard(board) {
    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            if (board[i][j] != 0) {

                arr[i][j].innerText = board[i][j]
            }

            else
                arr[i][j].innerText = ''
        }
    }
}


button.onclick = function () {
    var xhrRequest = new XMLHttpRequest()
    xhrRequest.onload = function () {
        var response = JSON.parse(xhrRequest.response)
        console.log(response)
        initializeTemp(temp)
        resetColor()

        board = response.board
        setTemp(board, temp)
        setColor(temp)
        changeBoard(board)
    }
    xhrRequest.open('get', 'https://sugoku.herokuapp.com/board?difficulty=easy')
    //we can change the difficulty of the puzzle the allowed values of difficulty are easy, medium, hard and random
    xhrRequest.send()
}


function isSafe(board,r,c,no)
{
    //not repeating in the same row and column
    
    for(var i=0;i<9;i++)
        {
            if(board[i][c]==no or board[r][i]==no)
                {
                    return false;
                }
            
        }
    
    
    //subgrid
    var sx=r-r%3;
    var sy=c-c%3;
    
    for(var x=sx;x<sx+3;x++)
        {
            for(var y=sy;y<sy+3;y++)
                {
                    if(board[x][y]==no)
                        {
                            return false;
                        }
                }
        }
    
    return true;
}

// you can make a call to changeboard(board) function to update the state on the screen
function solveSudokuHelper(board,r,c){

    //base case 
    if(r==9){
        changeBoard(board);
        return true;
    }
    //other cases - write your code here
if(c==9)
    {
        return solveSudokuHelper(board,r+1,0);
    }
    //pre-filled cell skip it
    
    if(board[r][c]!=0)
        {
            return solveSudokuHelper(board,r,c+1);
        }
    
    //there is 0 in the current location
    
    for(var i=1;i<=9;i++)
        {
            if(isSafe(board,r,c,i))
                {
                    board[r][c]=i;
                    var success = solveSudokuHelper(board,r,c+1);
                    if(success==true)
                        {
                            return true;
                        }
                    
                    board[r][c]=0;
                    
                }
        }
    
    return false;
    
}
    
    

   







   //finish your code here

}

function solveSudoku(board) {
    solveSudokuHelper(board,0,0);
}


solve.onclick = function () {
    solveSudoku(board)
}