Question

I was thinking earlier today about an idea for a small game and stumbled upon how to implement it. The idea is that the player can make a series of moves that cause a little effect, but if done in a specific sequence would cause a greater effect. So far so good, this I know how to do. Obviously, I had to make it be more complicated (because we love to make it more complicated), so I thought that there could be more than one possible path for the sequence that would both cause greater effects, albeit different ones. Also, part of some sequences could be the beggining of other sequences, or even whole sequences could be contained by other bigger sequences. Now I don’t know for sure the best way to implement this. I had some ideas, though.

1) I could implement a circular n-linked list. But since the list of moves never end, I fear it might cause a stack overflow ™. The idea is that every node would have n children and upon receiving a command, it might lead you to one of his children or, if no children was available to such command, lead you back to the beggining. Upon arrival on any children, a couple of functions would be executed causing the small and big effect. This might, though, lead to a lot of duplicated nodes on the tree to cope up with all the possible sequences ending on that specific move with different effects, which might be a pain to maintain but I am not sure. I never tried something this complex on code, only theoretically. Does this algorithm exist and have a name? Is it a good idea?

2) I could implement a state machine. Then instead of wandering around a linked list, I’d have some giant nested switch that would call functions and update the machine state accordingly. Seems simpler to implement, but… well… doesn’t seem fun… nor ellegant. Giant switchs always seem ugly to me, but would this work better?

3) Suggestions? I am good, but I am far inexperienced. The good thing of the coding field is that no matter how weird your problem is, someone solved it in the past, but you must know where to look. Someone might have a better idea than those I had, and I really wanted to hear suggestions.

Answer 1

I’m not absolutely completely sure that I understand exactly what you’re saying, but as an analagous situation, say someone’s inputting an endless stream of numbers on the keyboard. ‘117’ is a magic sequence, ‘468’ is another one, ‘411799’ is another (which contains the first one).

So if the user enters:

55468411799

you want to fire ‘magic events’ at the *s:

55468*4117*99*

or something like that, right? If that’s analagous to the problem you’re talking about, then what about something like (Java-like pseudocode):

MagicSequence fireworks = new MagicSequence(new FireworksAction(), 1, 1, 7); MagicSequence playMusic = new MagicSequence(new MusicAction(), 4, 6, 8); MagicSequence fixUserADrink = new MagicSequence(new ManhattanAction(), 4, 1, 1, 7, 9, 9);  Collection<MagicSequence> sequences = ... all of the above ...;  while (true) {   int num = readNumberFromUser();   for (MagicSequence seq : sequences) {     seq.handleNumber(num);   } } 

while MagicSequence has something like:

Action action = ... populated from constructor ...; int[] sequence = ... populated from constructor ...; int position = 0;  public void handleNumber(int num) {   if (num == sequence[position]) {     // They've entered the next number in the sequence     position++;     if (position == sequence.length) {        // They've got it all!        action.fire();        position = 0; // Or disable this Sequence from accepting more numbers if it's a once-off     }   } else {     position = 0; // missed a number, start again!   } }