Longest Substring Without Repeating Characters

1def lengthOfLongestSubstring(s: str) -> int:
2    seen = {}
3    l = 0
4    res = 0
5    
6    for r in range(len(s)):
7        if s[r] in seen and seen[s[r]] >= l:
8            l = seen[s[r]] + 1
9        seen[s[r]] = r
10        res = max(res, r - l + 1)
11        
12    return res