784\. Letter Case Permutation

Medium

Given a string `s`, you can transform every letter individually to be lowercase or uppercase to create another string.

Return _a list of all possible strings we could create_. Return the output in **any order**.

**Example 1:**

**Input:** s = "a1b2"

**Output:** ["a1b2","a1B2","A1b2","A1B2"] 

**Example 2:**

**Input:** s = "3z4"

**Output:** ["3z4","3Z4"] 

**Constraints:**

*   `1 <= s.length <= 12`
*   `s` consists of lowercase English letters, uppercase English letters, and digits.