Problem

At Spotify, a text-processing utility stores strings as mutable character arrays. Write a function that reverses the array in place without allocating another array for the result.

Given a list of characters s, modify s so that its characters appear in reverse order.

Formal Specification

• Input: s — a list of single-character strings
• Output: Do not return a new list. Modify s directly and return None.

Examples

Example 1

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

Explanation: Swapping from both ends reverses the array in place.

Example 2

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

Explanation: The first and last characters are swapped, then the process continues inward.

Constraints

• 1 <= len(s) <= 10^5
• Each element of s is a single printable character
• You must use O(1) extra space
• The input list is mutable and should be modified directly