请教一个算法问题

Question

用的js
arr = [1,2,3,4,5,6,7,8,9]
怎么输出3个间隔做倒序
输出 [[3,2,1],[6,5,4],[9,8,7]]

Answer 1

const ary = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const result = Array.from(
  {length: Math.ceil(ary.length / 3)},
  (v, i) => ary.slice(i * 3, (i + 1) * 3).reverse(),
);

console.log(result);

Answer 2

const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const result = [];
for (let i=0,length=arr.length;i<length;i+=3) {
   result.push(arr.slice(i, i+3).reverse());
}