不要给另外的数组分配额外的空间，你必须原地修改输入数组、使用 O(1) 的额外空间解决这一问题。
你可以假设数组中的所有字符都是 ASCII 码表中的可打印字符。
示例 1： 输入：["h","e","l","l","o"] 输出：["o","l","l","e","h"] 示例 2： 输入：["H","a","n","n","a","h"] 输出：["h","a","n","n","a","H"]
class Solution:
def reverseString(self, li):
"""
Do not return anything, modify s in-place instead.
"""
start, end = 0, len(li) - 1
while start < end:
li[start], li[end] = li[end], li[start]
start += 1
end -= 1
return li
原文：https://www.cnblogs.com/a438842265/p/15019882.html