JavaScript generate random number except some values

Question

I\'m generating random numbers from 1 to 20 by calling generateRandom(). How can I exclude some values, say 8 and 15?

function generateRandom(mi         


        

Answer 1

I have answered a similar question for Java: Generate random numbers except certain values. I just copy and paste the answer as follows.

Actually, we do not need to use contains(random) with a while loop.

To simplify the question, let's see what happens if we only have one excluding value. We can split the result to 2 parts. Then the number of possible values is range-1. If the random number is less than the excluded value, just return it. Otherwise, we could add 1.

For multiple excluding values, We can split the result set into size+1 parts, where size means the number of excluding values. Then the number of possible values is range-size. Then we sort excluding values in ascending order. If random number is less than the excluding value minus i, then we just return the random number add i, where i is the index of the the excluding value.

public int generateRandomNumberWithExcepts(int start, int end, List excepts) {
    int size = excepts.size();
    int range = end - start + 1 - size;
    int randNum = random.nextInt(range) + start;
    excepts.sort(null); // sort excluding values in ascending order
    int i=0;
    for(int except : excepts) {
        if(randNum < except-i){
            return randNum + i;
        }
        i++;
    }
    return randNum + i;
}