Longest Substring Without Repeating Characters (write full main, include follow-ups)

Problem: Longest Substring Without Repeating Characters (must provide runnable main, include follow-ups) Given a string s, return the length of the longest contiguous substring that contains no repeated characters. Input (stdin) One line: string s (visible ASCII characters; no spaces) Output (stdout) One integer: the maximum length Constraints 0 <= len(s) <= 2 * 10^5 Follow-ups Output the substring itself (any one if multiple). If the input is a character stream, explain how to maintain the answer online and analyze memory usage. Example Input abcabcbb Output 3