Do you have in mind the good old TicTacToe?
Assuming that you get all the data in one array, you put a space around each value, | as a columns separator and multiple - as rows separator, with something like ["O", "X", " ", " ", "X", " ", "X", "O", " "] you should be returning this structure (inclusive of new lines):
O | X |
-----------
| X |
-----------
X | O |
Now, to spice up things a bit, we are going to expand our board well beyond a trivial 3 x 3 square and we will accept rectangles of big sizes, still all as a long linear array.
For example, for "O", "X", " ", " ", "X", " ", "X", "O", " ", "O"] (same as above, just one extra "O") and knowing that the length of each row is 5, you will be returning
O | X | | | X
-------------------
| X | O | | O
And worry not about missing elements, as the array/list/vector length is always going to be a multiple of the width.