leetcode-344 反转字符串

编写一个函数，其作用是将输入的字符串反转过来。输入字符串以字符数组 s 的形式给出。
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。

示例 1：
输入：s = ["h","e","l","l","o"]
输出：["o","l","l","e","h"]

示例 2：
输入：s = ["H","a","n","n","a","h"]
输出：["h","a","n","n","a","H"]
 
提示：
1 <= s.length <= 105
s[i] 都是 ASCII 码表中的可打印字符

解法一：（双指针）

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        i,r=0,len(s)-1
        while i<r:
            s[i],s[r]=s[r],s[i]
            i+=1
            r-=1

解法二：（切片，倒序）

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        s[:] = s[::-1]

解法三：（对称位置互换）

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        for i in range(len(s)//2):
            s[i],s[len(s)-1-i] = s[len(s)-1-i],s[i]