算法二：求解無重複字符的最長子串

該代碼實現的思路來自leetcode

int lengthOfLongestSubstring(string s) {
       if(s.empty())
       {
           return 0;
       }
       size_t size = s.size();
       int i = 0,j = 0;
       int len = 0;
       unordered_set<char> se;
       while(i<=size-1&&j<= size-1)
       {
           if((se.insert(s[j])).second)
           {
               j++;
               continue;
           }
           else
           {
               len = max(len,j-i);
               se.erase(s[i]);
               i++;
           }
       }
       return len;
   }