Longest Substring Without Repeating Characters

Given a string s, return the length of the longest substring without repeating characters.

Function signature

func LengthOfLongestSubstring(s string) int

Example

s = "abcabcbb"
output = 3

Constraints

• 0 <= len(s) <= 200_000
• s consists of ASCII characters

Notes

• Use a sliding window with a map of last‑seen indices.