class Solution {
public:
    int a[26];
    int longestSubstringWithoutDuplication(string s) {
       int res=0;
       for(int i=0,j=0;i<s.size();i++)
       {
           a[s[i]-'a']++;
           while(a[s[i]-'a']>1)
           {
               a[s[j]-'a']--;
               j++;
           }
           res=max(res,i-j+1);
       }
       return res;
    }
};