how to stack possible move for minimax algoritm?

hi..

i want to make a mini board game like tic tac toe in unity3d with minimax algoritm, but i cant determine how to stacking possible move to make the algoritm run well. the game has same board and rule as tic tac toe but it has different move and pieces. my game has 3 pieces which is placed in three edges to move until its make diagonal, vertical, or paralel line except its starting position. the starting position same as chess and the board like this.

i hope anyone can help me to find the best way to stacking next possible move.