A voucher code is a string code of lowercase letters, digits and dashes. The website accepts the code
with the letters in any mixture of upper and lower case. Return every string that the website would
accept, in any order. Digits and dashes never change.
Examples
Input: code = "a1b"
Output: ["a1b", "A1b", "a1B", "A1B"]
Input: code = "7-7"
Output: ["7-7"]
Input: code = ""
Output: [""]
Constraints
0 <= len(code) <= 10, at most 8 of them letters- The result therefore holds at most 256 strings.
Goals
- Branch two ways for letters and one way for other characters
- Build strings position by position with an index parameter