Real-world examples of recursion [closed]

Answer 1

In my job we have a system with a generic data structure that can be described as a tree. That means that recursion is a very effective technique to work with the data.

Solving it without recursion would require a lot of unnecessary code. The problem with recursion is that it is not easy to follow what happens. You really have to concentrate when following the flow of execution. But when it works the code is elegant and effective.

Answer 2

Recursion is used in things like BSP trees for collision detection in game development (and other similar areas).

Answer 3

I have a system that uses pure tail recursion in a few places to simulate a state machine.

Answer 4

People often sort stacks of documents using a recursive method. For example, imagine you are sorting 100 documents with names on them. First place documents into piles by the first letter, then sort each pile.

Looking up words in the dictionary is often performed by a binary-search-like technique, which is recursive.

In organizations, bosses often give commands to department heads, who in turn give commands to managers, and so on.

Answer 5

Recursion is appropriate whenever a problem can be solved by dividing it into sub-problems, that can use the same algorithm for solving them. Algorithms on trees and sorted lists are a natural fit. Many problems in computational geometry (and 3D games) can be solved recursively using binary space partitioning (BSP) trees, fat subdivisions, or other ways of dividing the world into sub-parts.

Recursion is also appropriate when you are trying to guarantee the correctness of an algorithm. Given a function that takes immutable inputs and returns a result that is a combination of recursive and non-recursive calls on the inputs, it's usually easy to prove the function is correct (or not) using mathematical induction. It's often intractable to do this with an iterative function or with inputs that may mutate. This can be useful when dealing with financial calculations and other applications where correctness is very important.

Answer 6

Parsers and compilers may be written in a recursive-descent method. Not the best way to do it, as tools like lex/yacc generate faster and more efficient parsers, but conceptually simple and easy to implement, so they remain common.