使用递归函数而不是循环。每次调用方法时，都应该在数组的较小部分上，并在length = 0时停止。这个链接应该可以帮助您设计功能。

Use a recursive function, instead of loops. Each time you call the method should be on a smaller portion of the array and stop when length = 0. This link should help you design your function.