class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if(s.empty())
            return 0;
        int ans = 1;
        size_t beg = 0, end = 1;
        vector<bool> visited(256, false);
        visited[s[0]] = true;
        while(end < s.size())
        {
            if(visited[s[end]])
            {
                while(1)
                {
                    visited[s[beg]] = false;
                    if(s[beg++] == s[end])
                        break;
                }
            }
            visited[s[end++]] = true;
            if(end - beg > ans)
                ans = end - beg;
        }

        return ans;
    }
};