https://leetcode.com/problems/reverse-string/
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"]