I need to solve 4x4 tic tac toe using alpha beta pruning, I have solved 3x3 tic tac toe using minimax, and it works very well, but in 4x4 minimax takes lot of time as search space is too big, so I am applying alpha beta pruning but I am not getting clear idea, that upto what depth I should go and what evaluation function should I write in order to give perfect game play, heuristic may also lead to false results and not perfect game play, so how do I ensure perfect game play for 4x4 using fast approach?? Any suggestions or approach will help me a lot. Looking forward to get some inputs.