The Longest Journey

Given a string s, imagine reading through it one character at a time, as if you’re following a path made of letters. As you move forward, you want to keep track of the longest stretch you can travel without encountering the same character twice. String s consists of English letters, digits, symbols and spaces.

Your task is to find the length of the longest substring without duplicate characters — in other words, the longest continuous portion of s where every character is unique and no repeats interrupt the journey.

Example 1:

Input:

s = "xyzxyzyyxxxx"

Output:

def longest_substring_length(s) -> 3

Explanation: The answer is "xyz", with the length of 3. Note that "yzx" and "zxy" are also correct answers.

Example 2:

Input:

s = "xxxxxxxxxxxxxx"

Output:

def longest_substring_length(s) -> 1

Explanation: The answer is "x", with the length of 1.

Constraints:

• 0 <= s.length <= 5 * 10^4