Random number generation

Question

I need a random number generation algorithm that generates a random number for a specific input. But it will generate the same number every time it gets the same input. If this kind of algorithm available in the internet or i have to build one. If exists and any one knows that please let me know. (c, c++ , java, c# or any pseudo code will help much)

Thanks in advance.

Answer 1

You may want to look at the built in Java class Random. The description fits what you want.

Answer 2

Some code like this should work for you:

MIN_VALUE + ((MAX_VALUE - MIN_VALUE +1) * RANDOM_INPUT / (MAX_VALUE + 1))

• MIN_VALUE - Lower Bound
• MAX_VALUE - Upper Bound
• RANDOM_INPUT - Input Number

Answer 3

Usually the standard implementation of random number generator depends on seed value. You can use standard random with seed value set to some hash function of your input.

C# example:

string input = "Foo";
Random rnd = new Random(input.GetHashCode());
int random = rnd.Next();

Answer 4

I would use a hash function like SHA or MD5, this will generate the same output for a given input every time.

An example to generate a hash in java is here.

Answer 5

The Mersenne Twister algorithm is a good predictable random number generator. There are implementations in most languages.

Answer 6

How about..

public int getRandonNumber()
{
   // decided by a roll of a dice. Can't get fairer than that!
   return 4;
}

Or did you want a random number each time?

:-)

Answer 7

All pseudo-random number generators (which is what most RNGs on computers are) will generate the same sequence of numbers from a starting input, the seed. So you can use whatever RNG is available in your programming language of choice.

Given that you want one sample from a given seed, I'd steer clear of Mersenne Twister and other complex RNGs that have good statistical properties since you don't need it. You could use a simple LCG, or you could use a hash function like MD5. One problem with LCG is that often for a small seed the next value is always in the same region since the modulo doesn't apply, so if your input value is typically small I'd use MD5 for example.