題目描述：
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"]
代碼實現（個人版）：
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：代碼可能會提示“Assigning result of a function call, where the function has no returnpylint(assignment-from-no-return)”，不用管它，因為題目明確要求不能返回任何對象，而且這個代碼是可以運行的。
如果是單純地完成列表中字符串的反轉，則只需要
s = s[::-1]
即可。但這里要注意一個問題：局部變量和全局變量的內存地址是相互獨立的。在上面那段代碼中，x = ['h','e','l','l','o'] 是全局變量，而 s 只是一個局部變量，s = s[::-1]只是對局部變量s進行了修改，並不影響全局變量x的值，此時調用函數后，最終輸出的仍為x = ['h','e','l','l','o']。
要想實現對全局變量的修改，在函數內部對局部變量進行修改時，必須加上局部變量的索引，這個時候相當於是對局部變量指向的地址中的內容進行修改，也就是對全局變量進行修改，這樣才能在不進行return的情況下對全局變量x進行反轉。
參考文獻：
[1] 在函數里面修改列表數據：https://blog.csdn.net/u010969910/article/details/82764372