답안

function mergeSort(arr){

  if (arr.length <= 1){
    return arr;
  }

  const mid = Math.floor(arr.length / 2);

  const left = arr.slice(0, mid);
  const right = arr.slice(mid);

  return merge(mergeSort(left), mergeSort(right));
}

function merge(left, right){
  let result = [];

  while (left.length && right.length){
    if (left[0] < right[0]){
      result.push(left.shift());
    } else {
      result.push(right.shift());
    }
  }
  while (left.length) {
    result.push(left.shift());
  }
  while (right.length) {
    result.push(right.shift());
  }

  return result;
}


const array = prompt('배열을 입력하세요').split(' ').map(n => parseInt(n, 10));


console.log(mergeSort(array));