0784. Letter Case Permutation

https://leetcode.com/problems/letter-case-permutation

Description

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.

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