leetcode 3 无重复字符的最长子串

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        set<char>ss;
        int left=0,right=0,ans=0;
        while(right<s.length())
        {
            while(right<s.length()&&!ss.count(s[right])) ss.insert(s[right++]);
            ans=max(ans,right-left);
            ss.erase(s[left++]);
        }
        return ans;
    }
};