# 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.

## ac

```java
```