LeetCode #3 - Longest Substring Without Repeating Characters\nGiven a string, find the length of the longest substring without repeating characters. For example, in the string 'abcabcbb', the answer is 3, with the substring being 'abc'.\n\n### Problem Statement\n```python\ndef length_of_longest_substring(s: str) -> int:\n```\n### Example 1\n**Input:** 'abcabcbb' \n**Output:** 3 \n**Explanation:** The longest substring is 'abc', which has length 3.\n\n### Example 2\n**Input:** 'bbbbb' \n**Output:** 1 \n**Explanation:** The longest substring is 'b', with length 1.\n\n### Constraints\n* 0 <= s.length <= 1000\n* s consists of English letters, digits, symbols and spaces.