https://www.hackerrank.com/challenges/greedy-florist/problem?h_l=interview&playlist_slugs%5B%5D=interview-preparation-kit&playlist_slugs%5B%5D=greedy-algorithms

Solution.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

import static java.util.stream.Collectors.toList;

public class Solution {

     public static void main(String[] args) throws IOException {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
//        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        String[] firstMultipleInput = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");

        int n = Integer.parseInt(firstMultipleInput[0]);

        int k = Integer.parseInt(firstMultipleInput[1]);

        String[] szPrices = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");

        final List<Integer> prices = Arrays.stream(szPrices).map(it -> Integer.parseInt(it)).collect(toList());
        prices.sort(Comparator.reverseOrder());

        int minimalCost = 0;
        int round = 0;
        int i = 0;
        while (i < n) {
//        for (int i = 0; i<n; i++){
            for (int j = 0; j < k; j++) {
                minimalCost += (round + 1) * prices.get(i);
                i++;
                if (i >= n) {
                    System.out.println(minimalCost);
                    return;
                }
            }
            round++;
        }
        System.out.println(minimalCost);
    }
}

15' (10' to understand the problem, <5' coding :-P )