064. LongestSubstringWithKUniques.java

class Solution {
    public int longestKSubstr(String s, int k) {

        Map<Character, Integer> map = new HashMap<>();
        int i = 0, j = 0, res = -1, countK = 0;
        int n = s.length();
        while (j < n) {
            char ch = s.charAt(j);
            if (map.containsKey(ch)) {
                map.put(ch, map.get(ch) + 1);
            } else {
                countK++;
                map.put(ch, 1);
            }

            if (countK < k)
                j++;
            else if (countK == k) {
                res = Math.max(res, j - i + 1);
                j++;
            } else {
                while (countK > k) {
                    int count = map.get(s.charAt(i));
                    if (count == 1) {
                        countK--;
                        map.remove(s.charAt(i));
                    } else
                        map.put(s.charAt(i), count - 1);

                    i++;
                }
                j++;
            }
        }
        return res;
    }
}