public static String isValid(String s) {
// Write your code here
    Map<Character,Integer> map = new HashMap<>();

    for(char c : s.toCharArray()){
        map.put(c,map.getOrDefault(c,0)+1);
    }

    TreeMap<Integer,Integer> count = new TreeMap<>();

    for(int i : map.values()){
        count.put(i,count.getOrDefault(i,0)+1);
    }
    System.out.println(map +" , " + count);
    if(count.size() == 1){
        return "YES";
    }else if(count.size() == 2){
        int key1 = count.firstKey();
        int key2 = count.lastKey();
        int value1 = count.get(key1);
        int value2 = count.get(key2);

        if((key1 == 1 && value1 == 1) ||
           (key2 - key1 == 1 && value2 == 1)){
               return "YES";
           }
    }
    return "NO";
}