Longest_Substring.cpp

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        
        unordered_map<char,int> index;
        int start=0,res=0;
        for(int i=0;i<s.length();i++){
            
            if (index.find(s[i]) != index.end() && index[s[i]] >= start)
                 start = index[s[i]] + 1;
            
            index[s[i]] = i;
            res=max(res,i-start+1);
        }
        
        return res;
    }
};