# [3. Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)

## 题目

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



Example 1:

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

Example 2:

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

Example 3:

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

## 题目大意


在一个字符串重寻找没有重复字母的最长子串。

## 解题思路

这一题和第 438 题，第 3 题，第 76 题，第 567 题类似，用的思想都是"滑动窗口"。

滑动窗口的右边界不断的右移，只要没有重复的字符，就持续向右扩大窗口边界。一旦出现了重复字符，就需要缩小左边界，直到重复的字符移出了左边界，然后继续移动滑动窗口的右边界。以此类推，每次移动需要计算当前长度，并判断是否需要更新最大长度，最终最大的值就是题目中的所求。