Question

I have a function that is recursively calling itself, and i want to detect and terminate if goes into an infinite loop, i.e – getting called for the same problem again. What is the easiest way to do that?

EDIT: This is the function, and it will get called recursively with different values of x and y. i want to terminate if in a recursive call, the value of the pair (x,y) is repeated.

int fromPos(int [] arr, int x, int y)

Answer 1

If the function is purely functional, i.e. it has no state or side effects, then you could keep a Set of the arguments (edit: seeing your edit, you would keep a Set of pairs of (x,y) ) that it has been called with, and every time just check if the current argument is in the set. That way, you can detect a cycle if you run into it pretty quickly. But if the argument space is big and it takes a long time to get to a repeat, you may run out of your memory before you detect a cycle. In general, of course, you can’t do it because this is the halting problem.