notes/OJ notes/pages/Leetcode Letter-Case-Combination.md

# Leetcode Letter-Case-Combination

#### 2022-07-20 14:19

> ##### Algorithms:
>
> #algorithm #backtrack
>
> ##### Difficulty:
>
> #coding_problem #difficulty_medium
>
> ##### Additional tags:
>
> #leetcode
>
> ##### Revisions:
>
> N/A

##### Related topics:

##### Links:

- [Link to problem](https://leetcode.com/problems/letter-case-permutation/)

---

### Problem

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**.

#### Examples

**Example 1:**

```
**Input:** s = "a1b2"
**Output:** ["a1b2","a1B2","A1b2","A1B2"]
```

**Example 2:**

```
**Input:** s = "3z4"
**Output:** ["3z4","3Z4"]
```

#### Constraints

**Constraints:**

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

### Thoughts

> [!summary]
> This is a #backtrack problem.

### Solution