I'm making my own 5 in a row game where the board is bigger than 5x5, the size isn't decided but let's say 10x10. I'm designing this with a minimax algorithm and alfa-beta pruning. I've decided that a winning situation has the utility function of: (empty places + chosen place)*5, so if computer finds a win where there will be 2 empty places left then the value will be (2+1)*5 = 15. Same calculation for lose but times -5 instead of 5. For a draw it'll evaluate 0. Now, the issue that I'm writing this for is this: How do I determine the utility for an unfinished scenario where the depth limit is reached? Simply making it 0 isn't good enough, there must be some kind of "guess" or ranking.
An idea I had was to count all the X's in every row, every column and every possible diagonal and do empty places+chosen place times biggest found sequence of X's. The issue there is that the calculations take time and are a pain to write and then you'd also have to take into account the edges of the sequences found: are they bordered by O's? Should we count X's with empty gaps?
It seems awfully complicated and I wondered therefore if anyone has any good advise for me in regards to the unfinished scenarios. Thank you!
I have no idea what you are talking about in your first paragraph, a win should be scored as a win (minus depth to always find shortest win). If I understand you correctly you are looking to create an evaluation/heuristics function to be able to input a board state and output a static score for that state? Gomoku (5 in a row) is a popular game that has many engines, Google "evaluation function gomoku" and you will find lots of information and paper on the subject.
For a game like chess the evaluation is done e.g. by counting each sides material balance, piece positions, king safety etc. For X-in-a-row the usual approach is to give all possible scenarios a score and then add them up together. The scenarios for Gomoku are usually as follows:
Open means there are no blocking enemy pieces next to the friendly pieces:
OpenThree: -O--XXX---
ClosedThree: --OXXX---
How to sum them all up, and what score to give each scenario, is up to you and that is where the fun and experimenting begins!