Real-world examples of recursion [closed]

Answer 1

Phone and cable companies maintain a model of their wiring topology, which in effect is a large network or graph. Recursion is one way to traverse this model when you want to find all parent or all child elements.

Since recursion is expensive from a processing and memory perspective, this step is commonly only performed when the topology is changed and the result is stored in a modified pre-ordered list format.

Answer 2

There are lots of mathy examples here, but you wanted a real world example, so with a bit of thinking, this is possibly the best I can offer:

You find a person who has contracted a given contageous infection, which is non fatal, and fixes itself quickly( Type A) , Except for one in 5 people ( We'll call these type B ) who become permanently infected with it and shows no symptoms and merely acts a spreader.

This creates quite annoying waves of havoc when ever type B infects a multitude of type A.

Your task is to track down all the type Bs and immunise them to stop the backbone of the disease. Unfortunately tho, you cant administer a nationwide cure to all, because the people who are typeAs are also deadly allergic to the cure that works for type B.

The way you would do this, would be social discovery, given an infected person(Type A), choose all their contacts in the last week, marking each contact on a heap. When you test a person is infected, add them to the "follow up" queue. When a person is a type B, add them to the "follow up" at the head ( because you want to stop this fast ).

After processing a given person, select the person from the front of the queue and apply immunization if needed. Get all their contacts previously unvisited, and then test to see if they're infected.

Repeat until the queue of infected people becomes 0, and then wait for another outbreak..

( Ok, this is a bit iterative, but its an iterative way of solving a recursive problem, in this case, breadth first traversal of a population base trying to discover likely paths to problems, and besides, iterative solutions are often faster and more effective, and I compulsively remove recursion everywhere so much its become instinctive. .... dammit! )

Answer 3

• Parsing an XML file.
• Efficient search in multi-dimensional spaces. E. g. quad-trees in 2D, oct-trees in 3D, kd-trees, etc.
• Hierarchical clustering.
• Come to think of it, traversing any hierarchical structure naturally lends itself to recursion.
• Template metaprogramming in C++, where there are no loops and recursion is the only way.

Answer 4

Real world requirement I got recently:

Requirement A: Implement this feature after thoroughly understanding Requirement A.

Answer 5

XML, or traversing anything that is a tree. Although, to be honest, I pretty much never use recursion in my job.

Answer 6

Inductive reasoning, the process of concept-formation, is recursive in nature. Your brain does it all the time, in the real world.