Longest Substring Without Repeating

Problem: Longest substring without repeating characters.

function lengthOfLongestSubstring(s):
    charSet = empty set
    left = 0, maxLen = 0

    for right from 0 to s.length - 1:
        while s[right] in charSet:
            charSet.remove(s[left])
            left++
        charSet.add(s[right])
        maxLen = max(maxLen, right - left + 1)

    return maxLen

Example: "abcabcbb" → max $3$ ("abc").

Time: $O(n)$. Space: $O(\min(n, alphabet))$.