Random number with Probabilities

Question

I am wondering what would be the best way (e.g. in Java) to generate random numbers within a particular range where each number has a certain probability to occur or not?

Answer 1

If you have performance issue instead of searching all the n values O(n)

you could perform binary search which costs O(log n)

Random r=new Random();      
double[] weights=new double[]{0.1,0.1+0.2,0.1+0.2+0.5};
// end of init
double random=r.nextDouble();
// next perform the binary search in weights array

you only need to access log2(weights.length) in average if you have a lot of weights elements.