class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        if(s.length() == 0) return 0;

        unordered_map<char, int> table;
        int begin = 0, end = 0, len = 0, counter = 0;

        while(end < s.length()){
            char current = s[end];

            table[current]++;
            if(table[current] == 1) counter++;

            end++;

            while(counter > 2){
                char startchar = s[begin];

                if(table.count(startchar) == 1){
                    table[startchar]--;
                    if(table[startchar] == 0) counter--;
                }

                begin++;
            }

            len = max(len, end - begin);
        }

         return len;
    }
};