public static String isValid(String s) {

    int []rows = new int[26];
    for(int i=0; i<s.length();i++) {
        rows[s.charAt(i) - 'a']++;
    }

    HashMap<Integer, Integer> bank = new HashMap<>();
    for(int i=0; i<rows.length;i++) {
        if(rows[i] > 0) {
            bank.put(rows[i], bank.getOrDefault(rows[i], 0)+1);
        }
    }

    System.out.print(bank);

    if(bank.size() == 1) return "YES";
    else if(bank.size() == 2) {
        List<Integer> store = new ArrayList(bank.keySet());
        Collections.sort(store);
        if(store.get(0) == 1 && bank.get(1) == 1) return "YES";
        if(store.get(0) == store.get(1)-1 && 
            (bank.get(store.get(0)) == 1 || bank.get(store.get(1)) == 1 )) return "YES";
    }
    return "NO";

}