Can you help me choose the correct data structure?

Question

Hello everyone. I am working on a programming exercise. I should output symbol of the player that would win a tic tac toe game (on paper with unlimited space). I get input in this format:
X 5 2
O 5 3
X 7 4
O 6 3
...
The numbers are x and y coordinades of the ticked cell.
My problem is, I don't know which data structure should I use to save loaded moves. Currently I use custom class for all checked cells. The class stores symbol of the player (O or X), x and y coordiates of the cell and reference to all 8 cells touching it (if checked). I store all the cell objects in a list, but I feel there is a better solution.
I need to check if there are 5 symbols of the same player in any direction after each move. The game can have up to 500.000 rounds and the cootrdinates have values 0 to 1.000.000 in both x and y directions.

Answer 1

Maybe matrixes/lists? Just remember that nothing is unlimited, you may add a limit anywhere.