Longest Substring Without Repeating Characters

Problem Find the length of the longest substring of s with no repeated characters.

Input / Output

• Input: string s. Output: max length.

Constraints

• |s| up to 5*10^4; O(n) expected.

Example

• "abcabcbb" → 3 ("abc"); "bbbbb" → 1; "pwwkew" → 3 ("wke" — substring, not subsequence).

Expected approach

• Sliding window with last-seen-index map: for each right index, if s[r] was seen inside the current window, jump left to lastSeen[s[r]] + 1 (never move left backwards — the max() guard is the classic bug); update the answer each step. O(n) time, O(alphabet) space. The count-map + shrink-loop variant is equivalent; the index-jump version avoids the inner loop.