function sort(input) {
  let result = [];
  
  Object.keys(input).forEach((key) => {
    let indexes = input[key];
    
    indexes.forEach((index) => {
      result[index] = key;
    });
  });
  
  return result.join('');
}

const input = {
  ' ': [5],
  d: [10],
  e: [1],
  h: [0],
  l: [2, 3, 9],
  o: [4, 7],
  r: [8],
  w: [6],
};
Object.values(Object.entries(input).reduce((acc, [key, val]) => {
  val.forEach((idx) => {
    acc[idx] = key
  })
  return acc
}, {})).join('')

Object.keys(input).forEach(key => input[key].forEach(n => arr[n] = key))

const arr = [];
Object.keys(input).forEach(key => input[key].forEach(n => arr[n] = key));
console.log(arr.join(''))

const input = {
  ' ': [5],
  d: [10],
  e: [1],
  h: [0],
  l: [2, 3, 9],
  o: [4, 7],
  r: [8],
  w: [6],
};
const arr = [];
Object.keys(input).forEach(key => input[key].forEach(n => arr[n] = key));
console.log(arr.join(''));

const obj= {
  ' ': [5],
  d: [10],
  e: [1],
  h: [0],
  l: [2, 3, 9],
  o: [4, 7],
  r: [8],
  w: [6],
};
Object.entries(obj).reduce((a, [k, v]) => (v.map(i => a[i] = k), a), []).join("")