piles.js

const maxWeight = 50;
const piles = [
  {
    count: 60,
    weight: 10
  },
  {
    count: 120,
    weight: 30
  },
  {
    count: 100,
    weight: 20
  }
];
let bucket = [];

function getBucketWeight(bucket) {
  return bucket.reduce((weight, pile) => { return weight + pile.weight }, 0);
}

function getBucketCount(bucket) {
  return bucket.reduce((count, pile) => { return count + pile.count }, 0);
}

piles.forEach((pile) => {
  pile.ratio = pile.count / pile.weight;
});


piles.sort((a, b) => {
  if (a.ratio < b.ratio) {
    return -1;
  }

  if (a.ratio > b.ratio) {
    return 1;
  }

  return 0;
});


piles.forEach((pile) => {
  if (getBucketWeight(bucket) + pile.weight <= maxWeight) {
    bucket.push(pile);
  }
});

console.log(`Bucket weighs ${getBucketWeight(bucket)} with ${getBucketCount(bucket)} rocks.`);