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

A litte late to the show, but I found this a fun task to think about so here you go. My approach does not need to create all partitions, it also does not rely on pure luck of finding a random match, it is compact and it should be unbiased.

It works efficiently even when large values are used, as long as max is not too limiting.

const len = 4;
const total = 10;
const max = 4;

let arr = new Array(len);
let sum = 0;
do {
  // get some random numbers
  for (let i = 0; i < len; i++) {
    arr[i] = Math.random();
  }
  // get the total of the random numbers
  sum = arr.reduce((acc, val) => acc + val, 0);
  // compute the scale to use on the numbers
  const scale = (total - len) / sum;
  // scale the array
  arr = arr.map(val => Math.min(max, Math.round(val * scale) + 1));
  // re-compute the sum
  sum = arr.reduce((acc, val) => acc + val, 0);
  // loop if the sum is not exactly the expected total due to scale rounding effects
} while (sum - total);

console.log(arr);