Algorithm for random numbers generation - node.js

Question

I don't know which algorithm should I use. If it's necessary the platform is Node.js.
Volume = 100; Range = 5...15; N = 10.
I need to generate N numbers from Range that in sum will give Volume. What is the best way to do it?

Answer 1

Here's a quick, naive implementation.
There might be a numerical trick that allows making this faster, but this works. :)
Note that it's of course possible to pass in a combination of parameters that makes this function never complete, but for total = 100, min = 5, max = 15, n = 10 it does find solutions, e.g.
[ 14, 5, 11, 6, 10, 13, 9, 13, 14, 5 ]
[ 15, 13, 14, 10, 9, 8, 10, 8, 6, 7 ]
[ 8, 11, 11, 9, 12, 15, 5, 9, 6, 14 ]
[ 9, 12, 11, 6, 14, 12, 10, 7, 11, 8 ]
[ 9, 8, 9, 10, 11, 10, 12, 7, 14, 10 ]
[ 9, 9, 5, 14, 10, 13, 11, 13, 9, 7 ]
function generateNumbers(total, min, max, n) {
while (true) {
const numbers = [];
let sum = 0;
while (true) {
let num;
if (numbers.length === n - 1) {
// Fill in the last number with the remainder to satisfy the problem
num = total - sum;
if (num < min || num === 0 || num > max) {
// Out of bounds, this solution is invalid
break; // Try again.
}
} else {
num = Math.floor(min + Math.random() * (max + 1 - min));
}
numbers.push(num);
sum += num;
if (numbers.length === n && sum === total) {
// Solution found.
return numbers;
}
if (sum > total) {
// Overshot, retry.
break;
}
}
}
}
console.log(generateNumbers(100, 5, 15, 10));