# Past Challenges

## 42. Longest Substring Without Repeating Characters

94%

Write a function `solve` that finds the length of the longest substring without repeating characters.

**Example:** `Input: "abcabcbb"` `Output: 3` `Explanation: The answer is "abc", with the length of 3.`

Make sure you `return` your solution, don't print!

```python

def solve(s):
    pass
```