Thread: Random 0/1 with given possibility

I look over util.random and math.random, but I was't able to find anything, that would allow me to set the probability.

Originally Posted by juwan

I look over util.random and math.random, but I was't able to find anything, that would allow me to set the probability.

Say you have a 6-sided die, and you wanted to use it to decide something with a 5/6 chance of happening in one roll. What would you do?

I don't believe there is a function or utility (that I know of) which allows you to alter the probability distribution of the random output. To do so manually could get tricky but in this case is relatively easy. Get a random fraction value (using Random class posted above), skew this value by adding the appropriate probability distribution value, and cast this to an integer.

I've solved my problem:

p = 0,7 (user input)

int random1 = (double) (Math.random());
int win = 0;
if(random1 < p){
win = 1;
}

int totalOnes = 0;
double iterations = 100000000;
Random random = new Random();
for (int i = 0; i < iterations; i++) {
int zeroOrOneWithPointSevenProbabilityOfOne = random.nextInt(10) < 3 ? 0 : 1;
  if (zeroOrOneWithPointSevenProbabilityOfOne == 1) totalOnes++;
}
System.out.println(totalOnes + " (" + totalOnes / iterations + ")");

db