[Leetcode] 3.Longest Substring Without Repeating Characters（unordered_map）

通过把未访问的结点放到unordered_map中来判断是否重复，代码如下：

 class Solution {
 public:
     int lengthOfLongestSubstring(string s) {
         if(s == "")
             return ;
         unordered_map<char,int> hash;
         int len = ;
         int res = ;
         for(int i = ;i < s.length();i ++)
         {
             if(hash.find(s[i]) != hash.end())
             {
                 i = hash[s[i]];
                 hash.clear();
                 len = ;
             }
             else
             {
                 hash[s[i]] = i;
                 len ++;
                 res = max(len, res);
             }
         }
         return res;
     }
 };