Split number into 4 random numbers

Question

I want to split 10 into an array of 4 random numbers, but neither can be 0 or higher than 4. For example [1,2,3,4],

Answer 1

Given that:

In a collection of n positive numbers that sum up to S, at least one of them will be less than S divided by n (S/n)

and that you want a result set of exactly 4 numbers,

you could use the following algorithm:

1. Get a random number from range [1, floor(S/n)], in this case floor(10/4) = 2, so get a random number in the range of [1,2]. Lets mark it as x1.
2. Get a random number from range [1, floor((S - x1)/(n - 1))]. Lets mark it as x2.
3. Get a random number from range [1, floor((S - x1 - x2)/(n - 2))].
4. Continue until you get x(n-1).
5. Get the last number by doing S - x1 - x2 .... - x(n-1).

Finally, extend the above algorithm with a condition to limit the upper limit of the random numbers.

In n steps, you can get a collection.

    function getRandomInt(min, max) {
       return Math.floor(Math.random() * (max - min + 1)) + min;
    }

    function getRandomCollection(min, max, length, sum) {
        var collection = [];
        var leftSum = sum - (min - 1);

        for(var i = 0; i < length - 1; i++) {
             var number = getRandomInt(min, Math.min(Math.ceil(leftSum/(length - i)), max));
             leftSum -= number;
             collection.push(number);
        }
        leftSum += min - 1;
        while(leftSum > max) {
             var randomIndex = Math.floor(Math.random() * collection.length);
             if(collection[randomIndex] < max) {
                  collection[randomIndex]++;
                  leftSum--;
             }
        }
        
        collection.push(leftSum);
        return collection;
    }
    console.log(getRandomCollection(1, 4, 4, 10).join(' + ') + ' = 10');
    console.log(getRandomCollection(3, 20, 10, 100).join(' + ') + ' = 100');

Reference

My answer using the same algorithm for another question