Question

I was just wondering whether if it was possible to replace recursion with an explicit stack when you need the return value(s) and are comparing them to find the best solution (like dynamic programming)?

So something like (it doesn’t do anything, just an example):

int resursiveFunction (int state) { 

   if (known[state]) return cache[state];
   if (state == MAX_STATE) return 0;

   int max = 0;

   for (int i = 0 ; i < 5; i++) {
      int points = curPoints (state) + recursiveFunction (state+i);
      if (points > max) max = points; 
   }

   known[state] = true;
   cache[state] = max;
   return max; 

}

Answer 1

Yes. It’s possible.

Simply push and pop as appropriate. Recursion simply creates an ‘implicit stack’. You can unwind TCO’able recursive functions as well.

You may find Stacks and Recursion Elimination (it’s for a course) useful. It covers elimination (left-recursive) as well as emulation (stack).