CountLargestGroups.java

import java.util.HashMap;
import java.util.Map;

public class CountLargestGroups {
    public static int countLargestGroup(int n) {
        Map<Integer, Integer> map =new HashMap<>();
        int largestGrpSize = 0;

        for(int i=n;i>0;i--){
            int num = i;
            int sum = 0;
            while(num>0){
                sum += num%10;
                num = num/10;
            }
            int x = map.getOrDefault(sum, 0);
            map.put(sum, x+1);
            largestGrpSize = Math.max(largestGrpSize, x+1);
        }

        int countGrps = 0;
        for(Integer i: map.keySet()){
            if(map.get(i)==largestGrpSize)
                countGrps++;
        }
        return countGrps;
    }

    public static void main(String[] args) {
        System.out.println(countLargestGroup(15));
    }
}