class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int n =s.length();
        vector<int>charIndex(128,-1);
        int left = 0;
        int maxlen =0;
        for(int right =0;right<n;right++){
            if(charIndex[s[right]]>=left){
                left = charIndex[s[right]]+1;
            }
            charIndex[s[right]] = right;
            maxlen = max(maxlen, right-left+1);
        }
        return maxlen;

    }
};