K Unique String - JAVA

// Author : Saurav Kalsoor
// K Unique String - JAVA

import java.util.*;

public class Test {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        String s = sc.next();
        int k = sc.nextInt();

        System.out.println(kUniqueString(s, k));
    }

    public static int kUniqueString(String s, int k) {
        HashMap<Character, Integer> freq = new HashMap<>();

        for(int i = 0; i < s.length(); i++){
            freq.put(s.charAt(i), freq.getOrDefault(s.charAt(i), 0) + 1);
        }

        Set<MyPair> st = new TreeSet<>(new Comparator<MyPair>() {
            @Override
            public int compare(MyPair a, MyPair b) {
                if(a.frequency == b.frequency)
                    return a.ch - b.ch;
                return a.frequency - b.frequency;
            }
        });

        for(Map.Entry<Character, Integer> x : freq.entrySet()){
            st.add(new MyPair(x.getKey(), x.getValue()) );
        }

        int distinct = freq.size(), changes = 0;

        for(MyPair x : st){
            if(distinct <= k)
                break;

            changes += x.frequency;
            distinct--;
        }

        return changes;
    }

}

class MyPair{
    public char ch;
    public int frequency;

    public MyPair(char ch, int frequency){
        this.ch = ch;
        this.frequency = frequency;
    }
}