Longest Substring with At Most Two Distinct Characters

public int lengthOfLongestSubstringTwoDistinct(String s){
    Map<Character, Integer> mymap = new HashMap<>();
    int start =0, end = 0, count = 0, len = s.length();
    int maxLen = 0;
    while(end < len){
        char c = s.charAt(end);
        map.put(c, map.getOrDefault(c, 0) + 1);
        if(map.get(c) == 1) count++:
        end++
        while(count > 2){
            char q = s.charAt(start);
            map.put(q, map.getOrDefault(q, 0)-1);
            if(map.get(q)==0) count--; // as only way to achieve 0 is from 1 (that is subtracting 1 from 1 in earlier step can only create 0)
            start++;
        }
        maxLen = Math.max(maxLen, end -start);
    }
    return maxLen;
}