Question

I would like to know how to handle problems where there is a process which is used in many different ‘levels’ of a problem in c, preferable in an ‘idiomatic’ way.I know I did not explain this well enough, so let me give an example:

Consider the general problem of making a game solver, which is supposed to print the best next move.I think that it should check all possible moves in a for loop and see if it is a winning move(in this round) if it is, return the move, otherwise check every possible move the opponent can play against your move (for loop) and call the function to find the best move again.

However, I find that this approach has some limitations, such as performance (the program will spend it’s time running boilerplate code required to call the functions etc)
and limited flexibility , since the function will have to find a method to communicate with the caller how good a move was found.That is, if it could be done at all.

bestmove()
{
  for (;i<maxmove;i++)
   {
    if(checkifwinning(moves[i])) return;
    for (;n<maxopponentmove;n++)
     {
      bestmove();
     }
   }

I have been messing with haskell for a while now, so I am afraid that my mind is set on seeking recursive solutions.I hope that you can show me a way to write this function in a ‘c native’ way.

Answer 1

You are talking about searching a game tree to find a best move; you could use a standard algorithm like minimax. Your approach seems to be a depth-first search of the tree which terminates at the first winning move found; note that this won’t find the shortest path to a winning move nor does it guard against the opponent’s winning.

There are ways to speed up the searching of game trees such as alpha-beta pruning. Such a standard algorithm is the way to go – much better than worrying about the overhead of calling functions in C, etc. C function calls are not expensive. Beware of such “optimizations” when writing C code – the optimizer is likely to be better at such things anyway. At the very least, first write a version in the most straightforward way so you have something to benchmark against. Your job is to find a good algorithm.