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.

Ideas:

visited record the letters we see so far in the range[l, r], if s[r] not in visited, r += 1, else continue l += 1 until s[r] not in visited

Code:

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        ans, l, r, visited = 0, 0, 0, set()
        while r < len(s):
            if s[r] not in visited:
                visited.add(s[r])
                r += 1
            else:
                while s[r] in visited:
                    l_c = s[l]
                    visited.remove(l_c)
                    l += 1
            ans = max(ans, r - l)
        return ans