sudoku-solver.js

/**
 * @param {character[][]} board
 * @return {void} Do not return anything, modify board in-place instead.
 */

var solveSudoku = function(board) {
    
solve(board);
    
};

var solve = function (board) {
  for (var i = 0; i < 9; i++) {
    for (var j = 0; j < 9; j++) {
      if (board[i][j] !== '.') continue;
      for (var k = 1; k <= 9; k++) {
        if (isValid(board, i, j, '' + k)) {
            board[i][j] = '' + k;
          if (solve(board)) {
            return true;
          } else {
            board[i][j] = '.';
          }
        }
      }
      return false;
    }
  }
  return true;
};

var isValid = function (board, i, j, num) {
  for (var k = 0; k < 9; k++) {
    if (board[i][k] === num) return false;
    if (board[k][j] === num) return false;
    if (board[Math.floor(i / 3) * 3 + Math.floor(k / 3)][Math.floor(j / 3) * 3 + (k % 3)] === num) return false;
  }
    
  return true;
    
};