longest substring with at most k distinct characters

public int (String s, int k) {
    
    if (s == null || s.length() == 0)
        return 0;
    HashMap<Character, Integer> map = new HashMap<>();
    int left = 0, max = 0;
    for (int i = 0; i < s.length(); ++i) {
        char c = s.charAt(i);
        if (map.containsKey(c)) {
            map.put(c, map.get(c) + 1);
        } else {
            map.put(c, 1);
            while (map.size() > k) {
                c = s.charAt(left++);
                map.put(c, map.get(c) - 1);
                if (map.get(c) == 0) {
                    map.remove(c);
                }
            }
        }
        max = Math.max(max, i - left + 1);
    }
    return max;
}

public int (String s, int k) {
    
    if (s == null || s.length() == 0)
        return 0;
    HashMap<Character, Integer> map = new HashMap<>();
    int left = 0, count = 0, max = 0;
    for (int i = 0; i < s.length(); ++i) {
        char c = s.charAt(i);
        if (map.containsKey(c)) {
            map.put(c, map.get(c) + 1);
        } else {
            map.put(c, 1);
            ++count;
        }
        if (count == k) {
            int len = i - left + 1;
            max = Math.max(len, max);
            // move left
            while (map.containsKey(s.charAt(left)) && map.get(s.charAt(left)) > 0) {
                map.put(s.charAt(left), map.get(s.charAt(left)) - 1);
            }
            map.remove(s.charAt(left));
            ++left;
            --count;
        }
    }
    return max;
}