public class DayCode {    public static void main(String[] args) {        String s = "baaabcb";        int k = 3;        int ans = new DayCode().longestSubstring(s, k);        System.out.println("ans is " + ans);    }
    /**     * https://leetcode-cn.com/problems/longest-substring-with-at-least-k-repeating-characters/     * @param s     * @param k     * @return     */    public int longestSubstring(String s, int k) {        if (s.length() < k) {            return 0;        }        HashMap<Character, Integer> counter = new HashMap<>(26);        for (int i = 0; i < s.length(); i++) {            counter.put(s.charAt(i), counter.getOrDefault(s.charAt(i), 0) + 1);        }        for (char c : counter.keySet()) {            if (counter.get(c) < k) {                int res = 0;                for (String t : s.split(String.valueOf(c))) {                    res = Math.max(res, longestSubstring(t, k));                }                return res;            }        }        return s.length();    }}