Algorithm for Math.Random [closed]

Question

This was the question asked by one Interviewer. I was unable to answer.

Question was, assume you want to pick a random number from the given array.

Condition is you are not supposed to pick anything in sequential and not to use built in Random function.

I have no idea. Like to know how is this Math.Random does for us?

I googled and didn't find the implementation/logic behind that.

Any one know?

Answer 1

So far three people have told you to use the last digit of Ticks. This doesn't work. Try doing so in a tight loop and you will quickly see why it is a bad idea.

The question is not very well posed. I like giving ambiguously posed questions in interviews because you get to find out how the candidate deals with an ambiguous situation. In this case I would immediately push back and find out what the interviewer means by "random". Is pseudo-randomness good enough? Is there a source of high-quality entropy available?

Once you have a clarified question it should be easier to answer.

The problem comes down to managing entropy. If you have a very weak source of entropy -- like the value of Ticks (not the last digit, which is worthless, but the entire value) then you can use that to seed a pseudo-random-number generator. If you have a high quality source of entropy then you can just use that to generate random bits directly.