LC 3. 无重复字符的最长子串

代码 :

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if(s.size() == 0) return 0;
        unordered_map<char, int> hash;
        int res = 0; 
        for(int i = 0, j = 0; j < s.size(); j ++ ) {
            hash[s[j]] ++;
            while(hash[s[j]] > 1) {
                hash[s[i++]]--;
            }
            res = max(res, j - i + 1);
        }
        return res;
    }
};