setting property values in Multi-dimensional object array

Question

I`m trying to initialize multi-array sudoku[9][9] which is consist of cell when I run sudoku.initialize(), all row, col, box in *sudoku[x][y]*s are 8,8,9 each.

  var cell = {
    sol: 0,
    row: 0,
    col: 0,
    box: 0,
    candi: [1, 2, 3, 4, 5, 6, 7, 8, 9]
};


var sudoku = {}
sudoku = new Array(9);
for (var i = 0; i < 9; i++) {
    sudoku[i] = new Array(9);
}
for (var i = 0; i < 9; i++) {
    for (var j = 0; j < 9; j++) {
        sudoku[i][j] = cell;
    }
}
sudoku.initialize = function () {
    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            sudoku[i][j].row = i;
            sudoku[i][j].col = j;
            if (i < 3) {
                if (j < 3)
                    sudoku[i][j].box = 1;
                else if (2 < j && j < 6)
                    sudoku[i][j].box = 2;
                else if (5 < j)
                    sudoku[i][j].box = 3;
            }
            else if (2 < i && i < 6) {
                if (j < 3)
                    sudoku[i][j].box = 4;
                else if (2 < j && j < 6)
                    sudoku[i][j].box = 5;
                else if (5 < j)
                    sudoku[i][j].box = 6;
            }
            else if (5 < i)
                if (j < 3)
                    sudoku[i][j].box = 7;
                else if (2 < j && j < 6)
                    sudoku[i][j].box = 8;
                else if (5 < j)
                    sudoku[i][j].box = 9;
        }
    }
}
sudoku.print=function(){
    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            document.write(sudoku[i][j].col + "&nbsp");
        }
        document.write("\n");
    }
}
sudoku.initialize();`

I guess there is misunderstand for multi-dementional array in javascript.

 sudoku[2][2].box=1
    1
    sudoku[4][8].box=2
    2
    sudoku[2][2].box
    2
    sudoku[3][3].box
    2

cuz I`m beginner for javascript, this codes could be ridiculous. but anyway you can catch what I meant.

All 81 items in your array point to the same object.

Yeldar Kurmangaliyev
– Yeldar Kurmangaliyev

2017-07-11 10:27:37 +00:00
Commented Jul 11, 2017 at 10:27 — Yeldar Kurmangaliyev
– Yeldar Kurmangaliyev, Commented Jul 11, 2017 at 10:27

Yeldar Kurmangaliyev · Accepted Answer · 2017-07-11 10:45:38Z

All 81 items in your multi-dimensional array point to the same object, because of this:

for (var i = 0; i < 9; i++) {
    for (var j = 0; j < 9; j++) {
        sudoku[i][j] = cell;
    }
}

You make sudoku[i][j] store a reference to the same object cell.
When you later try to modify / access values in sudoku[2][2], sudoku[3][3], sudoku[4][8], you actually work with the same object.

You need to create a new object for every cell.
Changing your code this way should help:

for (var i = 0; i < 9; i++) {
    for (var j = 0; j < 9; j++) {
        sudoku[i][j] = {
            sol: 0,
            row: 0,
            col: 0,
            box: 0,
            candi: [1, 2, 3, 4, 5, 6, 7, 8, 9]
        };
    }
}

You also don't need so many ifs in your initialize method.
Some math and integer division / modulus would do all the magic in two lines of code ;)

function Cell(row, col)
{
  this.col = col;
  this.row = row;
  this.sol = 0;
  this.box = Math.ceil(row / 3) * 3 + Math.ceil(col / 3) - 3;
  this.candidates = [1, 2, 3, 4, 5, 6, 7, 8, 9];
}

function Sudoku()
{
  this.rows = new Array(9);
  for (var i = 0; i < 9; i++) 
  {
    this.rows[i] = new Array(9);
    for (var j = 0; j < 9; j++) {
      this.rows[i][j] = new Cell(i, j);
    }
  }
  
  this.print = function() {
    for (var i = 0; i < 9; i++) {
        for (var j = 0; j < 9; j++) {
            document.write(this.rows[i][j].row + "/" + this.rows[i][j].col + "&nbsp");
        }
        document.write("<br/>");
    }
  };
}

var sudoku = new Sudoku();
sudoku.print();

Aurea · Accepted Answer · 2017-07-11 10:30:43Z

0

The problem is that you are assigning the same object to every one of your cells. Because objects in Javascript are stored by reference (not by value), doing

sudoku[1][2] = cell;

Essentially makes sudoku[1][2] and cell mean the same thing. You need to create a new cell object for every one of the positions in sudoku. There is a lot of material available on how to define "classes" in Javascript and instantiate objects, see for example:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

Although there are other approaches possible, for example you could clone the object, use prototypes, etc.

answered Jul 11, 2017 at 10:30

Aurea

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