题目描述：
Write a function that reverses a string. The input string is given as an array of characters char[].
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
You may assume all the characters consist of printable ascii characters.
Example 1:
Input: ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]
Example 2:
Input: ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]
代码实现（个人版）：
1 class Solution: 2 def reverseString(self, s) -> None: 3 """ 4 Do not return anything, modify s in-place instead. 5 """ 6 s[:] = s[::-1] 7 8 if __name__ == '__main__': 9 x = ['h','e','l','l','o'] 10 y = Solution().reverseString(x) 11 print(x)
注：代码可能会提示“Assigning result of a function call, where the function has no returnpylint(assignment-from-no-return)”，不用管它，因为题目明确要求不能返回任何对象，而且这个代码是可以运行的。
如果是单纯地完成列表中字符串的反转，则只需要
s = s[::-1]
即可。但这里要注意一个问题：局部变量和全局变量的内存地址是相互独立的。在上面那段代码中，x = ['h','e','l','l','o'] 是全局变量，而 s 只是一个局部变量，s = s[::-1]只是对局部变量s进行了修改，并不影响全局变量x的值，此时调用函数后，最终输出的仍为x = ['h','e','l','l','o']。
要想实现对全局变量的修改，在函数内部对局部变量进行修改时，必须加上局部变量的索引，这个时候相当于是对局部变量指向的地址中的内容进行修改，也就是对全局变量进行修改，这样才能在不进行return的情况下对全局变量x进行反转。
参考文献：
[1] 在函数里面修改列表数据：https://blog.csdn.net/u010969910/article/details/82764372