# Longest Substring Without Repeating Characters

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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.

**Example 4:**

**Input:** s = ""
**Output:** 0

**Constraints:**

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


[Source](https://leetcode.com/problems/longest-substring-without-repeating-characters/)