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# 无重复字符的最长子串
 [](https://imhuay.gitbook.io/studies/algorithms/problems/2022/02/pages/R5NyOzkn3qAZy7wCx1pS#中等) [](/studies/algorithms.md#leetcode) [](https://imhuay.gitbook.io/studies/algorithms/problems/2022/02/pages/R5NyOzkn3qAZy7wCx1pS#滑动窗口) [](/studies/algorithms.md#leetcode-hot-100)
**问题简述**
```
给定一个字符串 s ，请你找出其中不含有重复字符的 最长子串 的长度。
```
> [3. 无重复字符的最长子串 - 力扣（LeetCode）](https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/)
**思路：滑动窗口**
* 维护一个已经出现过的字符集合；
Python 写法1 （滑动窗口模板，推荐写法）
```python
class Solution:
def lengthOfLongestSubstring(self, s: str) -> int:
used = set()
l = r = 0 # 窗口边界
ret = 0
while r < len(s):
while s[r] in used: # 滑动左边界
# 判断的是右边界，移动的是左边界
used.remove(s[l])
l += 1
ret = max(ret, r - l + 1)
used.add(s[r])
r += 1
return ret
```
Python 写法2 （优化）
* **优化**：直接移动 l 指针到重复字符的下一个位置，减少 l 指针移动；
```python
class Solution:
def lengthOfLongestSubstring(self, s: str) -> int:
used = dict()
l = r = 0 # [l, r] 闭区间
ret = 0
while r < len(s):
if s[r] in used and l <= used[s[r]]: # l <= used[s[r]] 的意思是重复字符出现在窗口内；
l = used[s[r]] + 1
ret = max(ret, r - l + 1)
used[s[r]] = r
r += 1
return ret
```