Recursion or Iteration?

Question

Is there a performance hit if we use a loop instead of recursion or vice versa in algorithms where both can serve the same purpose? Eg: Check if the given string is a palind

Answer 1

It may be fun to write it as recursion, or as a practice.

However, if the code is to be used in production, you need to consider the possibility of stack overflow.

Tail recursion optimization can eliminate stack overflow, but do you want to go through the trouble of making it so, and you need to know you can count on it having the optimization in your environment.

Every time the algorithm recurses, how much is the data size or n reduced by?

If you are reducing the size of data or n by half every time you recurse, then in general you don't need to worry about stack overflow. Say, if it needs to be 4,000 level deep or 10,000 level deep for the program to stack overflow, then your data size need to be roughly 2⁴⁰⁰⁰ for your program to stack overflow. To put that into perspective, a biggest storage device recently can hold 2⁶¹ bytes, and if you have 2⁶¹ of such devices, you are only dealing with 2¹²² data size. If you are looking at all the atoms in the universe, it is estimated that it may be less than 2⁸⁴. If you need to deal with all the data in the universe and their states for every millisecond since the birth of the universe estimated to be 14 billion years ago, it may only be 2¹⁵³. So if your program can handle 2⁴⁰⁰⁰ units of data or n, you can handle all data in the universe and the program will not stack overflow. If you don't need to deal with numbers that are as big as 2⁴⁰⁰⁰ (a 4000-bit integer), then in general you don't need to worry about stack overflow.

However, if you reduce the size of data or n by a constant amount every time you recurse, then you can run into stack overflow when n becomes merely 20000. That is, the program runs well when n is 1000, and you think the program is good, and then the program stack overflows when some time in the future, when n is 5000 or 20000.

So if you have a possibility of stack overflow, try to make it an iterative solution.