class Solution {
public:
int lengthOfLongestSubstring(string s) {
unordered_set<char> lookup;
int n = s.size();
int maxstr= 0;
int left = 0;
for(int i = 0;i < n ;i ++){
while(lookup.find(s[i]) != lookup.end()){
lookup.erase(s[left]);
left++;
}
maxstr = max(maxstr,i-left+1);
lookup.insert(s[i]);
}
return maxstr;
}
};