문제 3. longest substring without repeating characters Given a string, find the length of the longest substring without repeating characters. Example 1:Input: "abcabcbb" Output: 3 Explanation: The answer is "abc", with the length of 3. Example 2:Input: "bbbbb" Output: 1 Explanation: The answer is "b", with the length of 1. Example 3:Input: "pwwkew" Output: 3 Explanation: The answer is "wke", with ..