Question

I have to pick an element from an ascending array. Smaller elements are considered better. So if I pick an element from the beginning of the array it’s considered a better choice. But at the same time I don’t want the choice to be deterministic and always the same element. So I’m looking for

a random numbers generator that produces numbers in range [0, n], but
the smaller the number is, the more chance of it being produced.

This came to my mind:

num = n;
while(/*the more iteration the more chance for smaller numbers*/)
  num = rand()%num;

I was wondering if anyone had a better solution.
I did look at some similar questions but they have details about random number generation generally. I’m looking for a solution to this specific type of random number generation, either an algorithm or a library that provides it.

Answer 1

Generate a Random number, say x, between [0,n) and then generate another Random floating point number, say y, between [0,1]. Then raise x to the power of y and use floor function, you’ll get your number.

int cust(int n)
{
  int x;
  double y, temp;
  x = rand() % n;
  y = (double)rand()/(double)RAND_MAX;
  temp = pow((double) x, y);
  temp = floor(temp);
  return (int)temp;
}

Update: Here are some sample results of calling the above function 10 times, with n = 10, 20 and 30.

2 5 1 0 1 0 1 4 1 0

1 2 4 1 1 2 3 5 17 6

1 19 2 1 2 20 5 1 6 6