Write the meme style where letters alternate case. Given a string s, return a copy where characters at even positions (0, 2, 4, ...) are uppercase and characters at odd positions are lowercase. Positions are counted over all characters, including spaces and punctuation, which are left as they are.
Examples
Input: s = "hello world"
Output: "HeLlO WoRlD"
Input: s = "PYTHON"
Output: "PyThOn"
Constraints
0 <= len(s) <= 2000smay contain letters, digits, spaces and punctuation
Goals
- Use `enumerate` or `range(len(s))` to know the position of each character
- Apply `upper` and `lower` selectively
- Build a string piece by piece