Friday, February 12, 2021

SKP's Java Problem Solving Series : Active Traders (HackerRank)

[Question/Problem Statement is the Property of HackerRank]

Algorithms/Data Structures - [Problem Solving] 
An Institutional Broker wants to Review their Book of Customers to see which are Most Acctive. Given a List of Trades By "Customer Name, Determine which Customers Account for At Least 5% of the Total Number of Trades. Order the List Alphabetically Ascending By Name."

n = 23
"customers = {"Bigcorp", "Bigcorp", "Acme", "Bigcorp", "Zork", "Zork", "Abe", "Bigcorp",  "Acme", "Bigcorp", "Bigcorp" , "Zork", "Bigcorp", "Zork", "Zork", "Bigcorp", "Acme", "Bigcorp", "Acme", "Bigcorp", "Acme",""Littlecorp" , "Nadircorp "}."

"Bigcorp had 10 Trades out of 23,which is 43.48% of the Total Trades."

"Both Acme and Zork had 5 trades,which is 21.74% of the Total Trades."

"The Littlecorp, Nadircorp and Abe had 1 Trade Each, which is 4.35%..."

"So the Answer is [""Acme"", "" Bigcorp  ,""Zork""] (In Alphabetical Order) Because only These Three Companies Placed atleast 5% of the Trades.

Function Description

Complete the Function mostActive in the Editor Below.

has the following parameter:
String customers[n] : An Array Customer Names

(Actual Question Says String Array, But Signature is List of Strings)

Returns String[] : An Alphabetically Ascending Array


• 1 < n < 10^5

• 1 < Length of customers[] < 20

• The First Character of customers[i] is a Capital English letter.

• All Characters of customers[i] except for the First One are Lowercase.

• Guaranteed that At least One Customer makes atleast 5% of Trades.

Input Format

"The First Line contains an integer, n, The Number of Elements in customers."       

"Each Line iof the n Subsequent Lines (where 0 s i< n) contains a string, customers[i]."      

Sample Case 0 Input For Custom Testing

Omega Alpha Omega Alpha Omega Alpha Omega Alpha Omega Alpha Omega Alpha Omega Alpha Omega Alpha Omega Alpha Omega Beta      

Function mostActive      
customers[] size n =  20       

customers[] = [As Provided Above]       

Sample Output





"Alpha made 10 Trades out of 20 (50% of the Total), Omega made 9 Trades (45% of the Total). and Beta made 1 Trade (5% of the Total).All of them have met the 5% Threshold, so all the Strings are Returned in an Alphabetically Ordered Array."        

[Explanation of the Solution]
This is Good Practice for the Brain for Problem Solving - Involves Simple Arithmetic and Mathematical Application. Ideally, A Programmer would want to Optimize the Solution in Space and Time (Which I Did Not :-)

[Source Code, Sumith Puri (c) 2021 - Free to Use & Distribute]
import static;
import static;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

* HackerRank Problem Solving - Ain't a Horse that Can't be Rode
* Sumith Kumar Puri (c) 2021 - ~ Bengaluru, Karnataka, India ~
class ActiveTradersLogic {

public static List<String> mostActive(List<String> customers) {

// How About Arrays or Custom LinkedList for a 'Very Fast' Traversal?
Map<String, Integer> customerMap = new TreeMap<String, Integer>();
List<String> solutionStr = new ArrayList<String>();
int customerMapSize = customers.size();

for (int i = 0; i < customerMapSize; i++) {

String customerKey = customers.get(i);

if (customerMap.containsKey(customerKey)) {

Integer customerCount = customerMap.get(customerKey);
customerMap.put(customerKey, ++customerCount);
} else {
customerMap.put(customerKey, 1);

Set<String> customerMapKeys = customerMap.keySet();
for (String customerKey : customerMapKeys) {

Integer customerCount = customerMap.get(customerKey);
double currentCustomerPercent = (double) (customerCount) / (double) customerMapSize;

if (currentCustomerPercent * 100 >= 5.0) {


return solutionStr;

public class ActiveTraders {


public static void main(String[] args) throws IOException {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(;
BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv(OUTPUT_PATH)));

int customersCount = Integer.parseInt(bufferedReader.readLine().trim());

List<String> customers = IntStream.range(0, customersCount).mapToObj(i -> {
try {
return bufferedReader.readLine();
} catch (IOException ex) {
throw new RuntimeException(ex);

List<String> result = ActiveTradersLogic.mostActive(customers);

bufferedWriter.write("\n")) + "\n");


Happy Problem Solving using Java!

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