Random number generation

I need a random number generation algorithm that generates a random number for a specific input. But it wi开发者_开发知识库ll 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.

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

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();

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.

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

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?

:-)

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

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.