3. 无重复字符的最长子串

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        unordered_set<char> s1;
        int maxl=0;
        for(int l=0,r=0;r<s.length();r++)
        {
            while(l<r&&(s1.count(s[r])==1))
            {
                s1.erase(s[l]);
                l++;
            }
            s1.insert(s[r]);
            if(s1.size()>maxl)
            {
                maxl=s1.size();
            }
        }
        return maxl;
    }
};