21. Longest Substring Without Repeating Characters
Given a string s, return the length of its longest substring without repeating characters.
範例 1:
輸入： s = "abcabcbb" 輸出： 3
範例 2:
輸入： s = "bbbbb" 輸出： 1
限制條件：
0 <= s.length <= 5 * 10^4
● 已自動儲存第 1 行，第 1 欄