/**
knakul853
**/

class Solution {
public:
    int lengthOfLongestSubstring(string s) {

        int n = (int)s.size();
        vector<int>dict(256, 0);
        int ans = INT_MIN;

         int i=0, j=0;

        while(i < n )
        {
            char c = s[i++];

            dict[c]++;

            while( j < i && dict[c] > 1 )
            {
                dict[s[j]]--;
                j++;
            }

            ans = max( ans, i - j );

        }

        if(ans == INT_MIN) return 0;;
        return ans;
    }
};