private void setWordsByCell(int i, int j) {
    wordsFromCell = new Bag<>();

    marked = new boolean[M][N];
    wordTo = new String[M][N];

    String letter = board.getLetter(i, j) + "";
    if (Objects.equals(letter, "Q")) {
      wordTo[i][j] = "QU";
    } else {
      wordTo[i][j] = letter;
    }

    dfs(i, j);
  }
  private void dfs(int i, int j) {
    marked[i][j] = true;
    if (wordTo[i][j].length() > 2 && dict.contains(wordTo[i][j])) {
      wordsFromCell.add(wordTo[i][j]);
    }

    if (dict.keysWithPrefix(wordTo[i][j]).iterator().hasNext()) {
      Iterable<int[]> adj = adj(i, j);
      for (int[] a : adj) {
        if (!marked[a[0]][a[1]]) {
          String letter = board.getLetter(a[0], a[1]) + "";
          if (Objects.equals(letter, "Q")) {
            wordTo[a[0]][a[1]] = wordTo[i][j] + "QU";
          } else {
            wordTo[a[0]][a[1]] = wordTo[i][j] + letter;
          }
          dfs(a[0], a[1]);
        }
      }
    }
    marked[i][j] = false;
  }