generate random numbers within a range with different probabilities

Question

How can i generate a random number between A = 1 and B = 10 where each number has a different probability?

Example: number / probability

1 - 20%

2 -

Answer 1

Assuming that you have a function p(n) that gives you the desired probability for a random number:

r = rand()  // a random number between 0 and 1
for i in A to B do
    if r < p(i) 
      return i
    r = r - p(i)    
done

A faster way is to create an array of (B - A) * 100 elements and populate it with numbers from A to B such that the ratio of the number of each item occurs in the array to the size of the array is its probability. You can then generate a uniform random number to get an index to the array and directly access the array to get your random number.