递归排序

function sort(arr) {
  let left = 0, right = arr.length - 1;
  if(arr.length === 1 || arr.length === 0) {
    return arr;
  }
  let mid = (left + right) >> 1;
  let leftArray = sort(arr.slice(left, mid + 1));
  let rightArray = sort(arr.slice(mid + 1));
  return merge(arr, leftArray, rightArray)
}
function merge(arr, leftArray, rightArray) {
  let leftLength = leftArray.length, leftIndex = 0;
  let rightLength = rightArray.length, rightIndex = 0;
  while(leftIndex < leftLength && rightIndex < rightLength) {
    if(leftArray[leftIndex] < rightArray[rightIndex]) {
      arr[leftIndex + rightIndex] = leftArray[leftIndex];
      leftIndex++;
    } else {
      arr[leftIndex + rightIndex] = rightArray[rightIndex];
      rightIndex++;
    }
  }
  while(leftIndex < leftLength) {
    arr[leftIndex + rightIndex] = leftArray[leftIndex];
    leftIndex++;
  }
  while(rightIndex < rightLength) {
    arr[leftIndex + rightIndex] = rightArray[rightIndex];
    rightIndex++;
  }
  return arr;
}
console.log(sort([5,3,8,4,2,7,1,6]))