Write a function that reverses a string. The input string is given as an array of characters `s`.

You must do this by modifying the input array [in-place](https://en.wikipedia.org/wiki/In-place_algorithm) with `O(1)` extra memory.

Example 1:
    
    Input: s = ["h","e","l","l","o"] Output: ["o","l","l","e","h"] 

Example 2:
    
    Input: s = ["H","a","n","n","a","h"] Output: ["h","a","n","n","a","H"] 

Constraints:

* `1 <= s.length <= 105`
* `s[i]` is a [printable ascii character](https://en.wikipedia.org/wiki/ASCII#Printable_characters).