# 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:**

<pre><code>Input: s = "a1b2"
<strong>Output:
</strong> ["a1b2","a1B2","A1b2","A1B2"]
</code></pre>

**Example 2:**

<pre><code>Input: s = "3z4"
<strong>Output:
</strong> ["3z4","3Z4"]
</code></pre>

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**Constraints:**

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