无重复字符的最长字串

class Solution{
public:
    int lengthOfLongestSubstring(std::string s){
        int begin = 0;
        int i = 0;//滑动窗口指针
        std::string word = "";
        int char_map[128] = {0};
        for(int i = 0; i < s.length(); i++){
            char_map[s[i]]++;
            if(char_map(s[i]) ==1){
                word + =s[i];
                if( result < word.length()){
                    result = word.length()
                }
            }
            else{
                while(begin < i && char_map[s[i]] > 1){
                    char_map[s[begin]]--;
                    begin ++;
                }
                word = "";
                for(int j = begin; j < =i; j++){
                    word += s[j];
                }
            }  
        }
        return result;
     }
};