1
var solveSudoku = function (board) {
2
  let intBoard = convertBoardToInteger(board);
3

4
  let y = 0,
5
    x = 0;
6

7
  while (y <= 8) {
8
    x = 0;
9
    while (x <= 8) {
10
      if (isFreeIndex(board, x, y)) {
11
        intBoard[y][x]++;
12
        while (!isPossibleValue(intBoard, x, y) && intBoard[y][x] < 10) {
13
          intBoard[y][x]++;
14
        }
15

16
        if (intBoard[y][x] > 9) {
17
          intBoard[y][x] = 0;
18
          let a = retraceBoard(board, x, y);
19
          (x = a[0]), (y = a[1]);
20
          x--;
21
        }
22
      }
23
      x++;
24
    }
25
    y++;
26
  }
27

28
  convertIntBoardToString(intBoard, board);
29
};
30

31
var isFreeIndex = function (board, x, y) {
32
  return board[y][x] == ".";
33
};
34

35
var isPossibleValue = function (intBoard, x, y) {
36
  return (
37
    isUniqueInColumn(intBoard, x, y) &&
38
    isUniqueOnRow(intBoard, x, y) &&
39
    isUniqueInBox(intBoard, x, y)
40
  );
41
};
42
var isUniqueOnRow = function (intBoard, x, y) {
43
  for (let i = 0; i < 9; i++) {
44
    if (intBoard[i][x] == intBoard[y][x] && i != y) {
45
      return false;
46
    }
47
  }
48
  return true;
49
};
50
var isUniqueInColumn = function (intBoard, x, y) {
51
  for (let i = 0; i < 9; i++) {
52
    if (intBoard[y][i] == intBoard[y][x] && i != x) {
53
      return false;
54
    }
55
  }
56
  return true;
57
};
58
var isUniqueInBox = function (intBoard, x, y) {
59
  let startX = x - (x % 3);
60
  let startY = y - (y % 3);
61

62
  for (let i = startX; i < startX + 3; i++) {
63
    for (let j = startY; j < startY + 3; j++) {
64
      if (intBoard[j][i] == intBoard[y][x] && (i != x || j != y)) {
65
        return false;
66
      }
67
    }
68
  }
69
  return true;
70
};
71

72
var retraceBoard = function (board, x, y) {
73
  do {
74
    if (x > 0) {
75
      x--;
76
    } else {
77
      x = 8;
78
      y--;
79
    }
80
  } while (board[y][x] != ".");
81
  return [x, y];
82
};
83

84
var convertBoardToInteger = function (board) {
85
  let intBoard = new Array(8);
86
  for (let y = 0; y < 9; y++) {
87
    intBoard[y] = new Array(8);
88
    for (let x = 0; x < 9; x++) {
89
      intBoard[y][x] = parseInt(board[y][x]);
90
      if (!intBoard[y][x]) intBoard[y][x] = 0;
91
    }
92
  }
93
  return intBoard;
94
};
95
var convertIntBoardToString = function (intBoard, board) {
96
  for (let y = 0; y < 9; y++) {
97
    for (let x = 0; x < 9; x++) {
98
      board[y][x] = intBoard[y][x].toString();
99
    }
100
  }
101

102
  return board;
103
};