Optimization - Jump Left Pointer

Jump left directly using a map of last positions.

function lengthOfLongestSubstring(s):
    charIndex = empty map
    left = 0, maxLen = 0

    for right from 0 to s.length - 1:
        if s[right] in charIndex and charIndex[s[right]] >= left:
            left = charIndex[s[right]] + 1
        charIndex[s[right]] = right
        maxLen = max(maxLen, right - left + 1)

    return maxLen

Improvement: Skip multiple characters at once instead of shrinking one by one.

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