Answer 1

Hello Tom

Answer 2

const reverseResult = [];
const reverseSort = arr => {
  console.log("begin: ", arr, reverseResult);
  if (reverseResult.length) {
    reverseResult.unshift(reverseResult.pop());
  }
  if (arr.length) {
    reverseResult.unshift(arr.pop());
    console.log("end: ", arr, reverseResult);
    if (arr.length) {
      reverseSort(arr);
    }
  }
};

Answer 3

function sortBalls (str) {
let arr = str.split('')
arr.sort((a, b) => {
return getNumByType(a) - getNumByType(b)
})

return arr.join('')

function getNumByType (type) {
  switch (type) {
    case '黄':
      return 1
    case '红':
      return 2
    default:
      return 3
  }
}

}