Random integer numbers with fixed sum

randomNumbersWithFixedSum.js

function arraySum(a) {
  return a.reduce((a, b) => a + b, 0)
}

function getRandomIntInclusive(min, max) {
  const minCeil = Math.ceil(min)
  const maxFloor = Math.floor(max)
  return Math.floor(Math.random() * (maxFloor - minCeil + 1)) + minCeil
}

function randomNumbersWithFixedSum(quantity, sum) {
  const randoms = [...Array(quantity - 1).keys()].map(q => getRandomIntInclusive(0, sum/quantity))
  const last = sum - arraySum(randoms)
  return [...randoms, last]
}

console.log(randomNumbersWithFixedSum(1, 100))
console.log(randomNumbersWithFixedSum(2, 100))
console.log(randomNumbersWithFixedSum(3, 100))
console.log(randomNumbersWithFixedSum(4, 100))
console.log(randomNumbersWithFixedSum(5, 100))