3. Longest Substring Without Repeating Characters

from collections import defaultdict
 
class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        l = 0
        count = 0
        ans = 0
        d = defaultdict(int)
        
        for r in range(len(s)):
            d[s[r]] += 1
            count += 1
            
            while d[s[r]] > 1:
                d[s[l]] -= 1
                l += 1
                count -= 1
               
            ans = max(ans, count)
        
        return ans

• classic sliding-window approach.
• we slide the right pointer forward until we see a duplicate character.
• then, we slide the left pointer forward until that character is no longer duplicated.
• keep a running max tally to return.

Categories:: string, hashmap, sliding-window