Leetcode 3. 无重复字符的最长子串

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int maxlen = 0;

        for(int i=0;i < s.size();i++){
            unordered_map<char,int> mp;
            mp[s[i]] = 1;
            int pos = i+1;
            while(pos < s.size()){
                if(mp[s[pos]] == 1){
                    break;
                }
                else{
                    mp[s[pos]] = 1;
                }
                pos++;
            }
            //cout << mp.size() <<" " << maxlen <<  endl;
            int mplen = mp.size();
            if(maxlen < mplen){
                maxlen = mp.size();
            }
            
        }
        return maxlen;
    }
};

__

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        unordered_set<char> st;
        int ans = 0;
        int rk = 1;
        for(int i=0;i < s.size();i++){
            st.insert(s[i]);
            if(i != 0){
                st.erase(s[i-1]);
            }
            while(rk < s.size()&&st.count(s[rk]) == 0){
                st.insert(s[rk]);
                rk++;
            }
            
            int stlen = st.size();
            if(stlen > ans) ans = stlen;
        }
        return ans;
    }
};

双指针法，而且不能直接用st.size()来比较