> For the complete documentation index, see [llms.txt](https://chiragjain.gitbook.io/neetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://chiragjain.gitbook.io/neetcode/3-longest-substring-without-repeating-characters.md).

# 3. Longest Substring Without Repeating Characters

## Medium

***

Given a string `s`, find the length of the **longest substring** without repeating characters.

 

**Example 1:**

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

**Example 2:**

```
Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.
```

**Example 3:**

```
Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.
```

 

**Constraints:**

* `0 <= s.length <= 5 * 104`
* `s` consists of English letters, digits, symbols and spaces.