LeetCode 3. Longest substring without duplicate characters

Given a string s , Please find out that there are no duplicate characters in it Longest substrings The length of .

Example 1:
Input : s = “abcabcbb”
Output : 3
explain : Because the longest substring without repeating characters is “abc”, So its length is 3.
Example 2:

Input : s = “bbbbb”
Output : 1
explain : Because the longest substring without repeating characters is “b”, So its length is 1.
Example 3:

Input : s = “pwwkew”
Output : 3
explain : Because the longest substring without repeating characters is “wke”, So its length is 3.
Please note that , Your answer must be Substring The length of ,“pwke” Is a subsequence , Not substring .

class Solution {
    
public:
    int lengthOfLongestSubstring(string s) {
    
        unordered_map<char, int> hash;
        int re = 0;
        /// j  rearwards ,i in front , from i and j Find the longest substring between , When finding the number of characters between >1 ,i Need to move back 
        for(int i = 0, j = 0; j < s.size(); j++)
        {
    
            hash[s[j]] ++;
            while(hash[s[j]] > 1) hash[s[i++]] --;
            re = max(re, j- i + 1);
        }
        return re;
    }
};