3. Longest Substring Without Repeating Characters

class Solution {public:        //判断字符c是否在字符串s中出现过    bool charInString(char c, string s)    {        for(int i = 0; i < s.size(); i++)            if(c == s.at(i))                return true;        return false;    }        //返回字符串s中以s.at(start)为开头的子字符串的长度    int oneSubStringLength(int start, string s)    {        string sub;        sub.push_back(s.at(start));        for(int i = start + 1; i < s.size(); i++)        {            if(charInString(s.at(i), sub))                return sub.size();            sub.push_back(s.at(i));        }        return sub.size();    }        //正片    int lengthOfLongestSubstring(string s)     {        if(s.size() == 0)            return 0;        int max = 1;        for(int i = 0; i < s.size(); i++)            if(max < oneSubStringLength(i, s))                max = oneSubStringLength(i, s);        return max;    }};