344. Reverse String

344. Reverse String

Easy

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"]

数组翻转

只需要将数组前一半和后面一半进行交换即可

Java

class Solution {
    public void reverseString(char[] s) {
        if(s == null || s.length == 0) return;
        int len = s.length/2;
        for(int i=0; i<len; i++){
            char temp = s[s.length-1-i];
            s[s.length-1-i] = s[i];
            s[i] = temp;
        }
    }
}

Python

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