DistrictTopAccounts.java

import java.util.Scanner;
import java.util.PriorityQueue;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

import java.io.FileInputStream;
import java.io.IOException;

public class DistrictTopAccounts {

    static PriorityQueue<Pair> pq;
    static TreeMap<Integer, PriorityQueue<Pair>> treemap = new TreeMap<>();
    
    public static void main(String... args) throws IOException {
        System.out.println("Executing DistrictTopAccounts... ");
        
        try (Scanner in = new Scanner(
                new FileInputStream(args[0]))) {
            String line;
            String delimiter = " ";
            while (in.hasNextLine()) {
                line = in.nextLine();

                String[] tokens = line.split(delimiter);
                int account_id  = Integer.parseInt(tokens[0]);
                int district_id = Integer.parseInt(tokens[1]);
                float balance   = Float.parseFloat(tokens[2]);
                
                Pair pair = new Pair(account_id, balance);
                PriorityQueue<Pair> accountBalance = treemap.get(district_id);
                if (accountBalance == null) {
                    accountBalance = new PriorityQueue<Pair>(4);
                    accountBalance.add(new Pair(account_id, balance));
                    treemap.put(district_id, accountBalance);
                }
                else {
                    accountBalance.add(pair);
					if (accountBalance.size() > 3)
						accountBalance.poll();
                }
            }
            System.out.println(treemap.size());
            
            // print the results
            for (Map.Entry<Integer, PriorityQueue<Pair>> entry : treemap.entrySet()) {
                System.out.print("District id : " + entry.getKey());
                System.out.print(". Top three accounts - ");
                for (Pair pair : entry.getValue()) {
                    System.out.print("account_id: " + pair.getKey() + " balance: " + pair.getValue() + " ");
                }
                System.out.println("");
            }
        }
    }
}