public boolean isValid(int val, int row, int col) {
    for (int j = 0;
         j < board[0].length;
         j++) {
      if (board[row][j] == val) {
        return false;
      }
    }
      else for (int i = 0;
                i < board.length;
                i++) {
        if (board[i][col] == val) {
          return false;
        }
      }
        else if ((row <= 3)  && (col <= 3)) {
          for (int j = 0;
               j < board[0].length;
               j++) {
            if (board[row][j] == val) {
              return false;
            }
          }
            else for (int i = 0;
                      i < board.length;
                      i++) {
              if (board[i][col] == val) {
                return false;
              }
            }
            else if ((row <= 3) && (col <= 6)) {
                for (int j = 0;
                     j < board[0].length;
                     j++) {
                  if (board[row][j] == val) {
                    return false;
                  }
                }
                  else for (int i = 0;
                            i < board.length;
                            i++) {
                    if (board[i][col] == val) {
                      return false;
                    }
                  }
                    else if ((row <= 3) && (col <= 9)) {
                      for (int j = 0;
                           j < board[0].length;
                           j++) {
                        if (board[row][j] == val) {
                          return false;
                        }
                      }
                      else for (int i = 0;
                                  i < board.length;
                                  i++) {
                          if (board[i][col] == val) {
                            return false;
                          }
                      }
                      else if ((row <= 6) && (col <= 3)) {
                            for (int j = 0;
                                 j < board[0].length;
                                 j++) {
                              if (board[row][j] == val) {
                                return false;
                              }
                            }
                            else for (int i = 0;
                                        i < board.length;
                                        i++) {
                                if (board[i][col] == val) {
                                  return false;
                                }
                            }
                            else if ((row <= 6) && (col <= 6)) {
                                  for (int j = 0;
                                       j < board[0].length;
                                       j++) {
                                    if (board[row][j] == val) {
                                      return false;
                                    }
                                  }
                                  else for (int i = 0;
                                              i < board.length;
                                              i++) {
                                      if (board[i][col] == val) {
                                        return false;
                                      }
                                  }
                                  else if ((row <= 6) && (col <= 9)) {
                                        for (int j = 0;
                                             j < board[0].length;
                                             j++) {
                                          if (board[row][j] == val) {
                                            return false;
                                          }
                                        }
                                        else for (int i = 0;
                                                    i < board.length;
                                                    i++) {
                                            if (board[i][col] == val) {
                                              return false;
                                            }
                                        }
                                        else if ((row <= 9) && (col <= 3)) {
                                              for (int j = 0;
                                                   j < board[0].length;
                                                   j++) {
                                                if (board[row][j] == val) {
                                                  return false;
                                                }
                                              }
                                              else for (int i = 0;
                                                          i < board.length;
                                                          i++) {
                                                  if (board[i][col] == val) {
                                                    return false;
                                                  }
                                              }
                                              else if ((row <= 9) && (col <= 6)) {
                                                    for (int j = 0;
                                                         j < board[0].length;
                                                         j++) {
                                                      if (board[row][j] == val) {
                                                        return false;
                                                      }
                                                    }
                                                    else for (int i = 0;
                                                                i < board.length;
                                                                i++) {
                                                        if (board[i][col] == val) {
                                                          return false;
                                                        }
                                                    }
                                                    else if ((row <= 9) && (col <= 9)) {
                                                          for (int j = 0;
                                                               j < board[0].length;
                                                               j++) {
                                                            if (board[row][j] == val) {
                                                              return false;
                                                            }
                                                          }
                                                          else for (int i = 0;
                                                                      i < board.length;
                                                                      i++) {
                                                              if (board[i][col] == val) {
                                                                return false;
                                                              }}}}}}}}}}}}return true;
    }
  }