bucket-of-rocks.js

function fillBucket(remainingWeight, piles, n) {
  if (n === 0 || remainingWeight === 0) {
    return 0;
  }

  const pile = piles[n - 1];
  if (pile.weight > remainingWeight) {
    return fillBucket(remainingWeight, piles, n - 1);
  }

  return Math.max(
    pile.count + fillBucket(remainingWeight - pile.weight, piles, n - 1),
    fillBucket(remainingWeight, piles, n - 1)
  );
}

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

console.log(fillBucket(maxWeight, piles, piles.length));