class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        //先得到字符串長度
        int s_len = s.length() - 1;
        int counti = 1; //從第二個開始查找
        int countj;
        int count_diff = 1; //計數(shù)不相同的字母
        int max_len = 1;    //最長長度一開始為1
        int down = 0;   //一開始從最底下開始查詢某個字母的是否在他前面有相同，遇見相同的就截斷，重新賦值down
        if ( s_len < 0)
            max_len = 0;
        else{
            while ( counti <= s_len ){  //一遍將s查詢完
                for ( countj = down; countj < counti; countj++){
                    if ( s[countj] != s[counti] ){
                        count_diff++;
                        if (max_len < count_diff){
                            max_len = count_diff;
                        }
                    }
                     else {
                         down = countj + 1; //從重復(fù)的字母后面哪一個開始查
                     }       
                }
                counti++;
                count_diff = 1; //重置計數(shù)器，以便于后面計算
            }
        }
        return max_len;         
    }
};