// Reverse String — EASY
// Category: string
Write a function that reverses a string. The input is given as an array of characters `s`.
You must do this by modifying the input array in-place with O(1) extra memory.
Hint: Use two pointers — one at the start and one at the end, swap, and move inward.
Example: s = ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]