How do 20 questions AI algorithms work?

Question

Simple online games of 20 questions powered by an eerily accurate AI.

How do they guess so well?

Answer 1

I recommend reading about the game here: http://en.wikipedia.org/wiki/Twenty_Questions

In particular the Computers section:

The game suggests that the information (as measured by Shannon's entropy statistic) required to identify an arbitrary object is about 20 bits. The game is often used as an example when teaching people about information theory. Mathematically, if each question is structured to eliminate half the objects, 20 questions will allow the questioner to distinguish between 2²⁰ or 1,048,576 subjects. Accordingly, the most effective strategy for Twenty Questions is to ask questions that will split the field of remaining possibilities roughly in half each time. The process is analogous to a binary search algorithm in computer science.