A requirement is to calculate the value of the board depending on the placement of pieces on the board.

• This function is often known as Evaluation Function.
• It is sometimes also called Heuristic Function.

The evaluation function is unique for every type of game.

The evaluation function is combined with the minimax function or alpha-beta pruning function and so on.

Evaluation

Evaluate all the available moves using minimax() or alpha-beta pruning() or similar.

Then returns the best move the maximizer can make.

function findBestMove(board):
  bestMove = NULL
  for each move in board :
    if current move is better than bestMove
      bestMove = current move
 
  return bestMove

To check whether the game is over and to make sure there are no moves left.

function isMovesLeft(board):
  for each cell in board:
    if current cell is empty:
      return true
 
  return false