Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string. Return a list of all possible strings we could create. You can return the output in any order. Example 1: Input: S = "a1b2" Output: ["a1b2","a1B2","A1b2","A1B2"] Example 2: Input: S = "3z4" Output: ["3z4","3Z4"] Example 3: Input: S = "12345" Output: ["12345"] Example 4: Input: S = "0" Output: ["0"] Constraints: S will be a string with length between 1 and 12. S will consist only of letters or digits.