Design Tic tac toe game
I think your interviewer meant that you can improve checking the winning situation and do it in \$O(1)\$ time by keeping track of the scores in rows, columns and both diagonals (total 8 variables for 3x3 board):

[row1, row2, row3, column1, column2, column3, diagonal, anti-diagonal]


Then, you can increment these value by 1 in case of "player 1" and decrement by one in case of "player 2". This will lead to only checking these 8 values (or you can also use the fact that you know where the last move took place) for 3 or -3 for a winning situation. You can find out more about this idea here.

Or, you can go over all the possible winning combinations like suggested here or here.