Fraudulent Activity Notifications in Algorithm | HackerRank Programming Solutions | HackerRank Problem Solving Solutions in Java [💯Correct]

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Introduction To Algorithm

The word Algorithm means “a process or set of rules to be followed in calculations or other problem-solving operations”. Therefore Algorithm refers to a set of rules/instructions that step-by-step define how a work is to be executed upon in order to get the expected results. 

Advantages of Algorithms:

  • It is easy to understand.
  • Algorithm is a step-wise representation of a solution to a given problem.
  • In Algorithm the problem is broken down into smaller pieces or steps hence, it is easier for the programmer to convert it into an actual program.

Link for the ProblemFraudulent Activity Notifications – Hacker Rank Solution

Fraudulent Activity Notifications – Hacker Rank Solution


HackerLand National Bank has a simple policy for warning clients about possible fraudulent account activity. If the amount spent by a client on a particular day is greater than or equal to  the client’s median spending for a trailing number of days, they send the client a notification about potential fraud. The bank doesn’t send the client any notifications until they have at least that trailing number of prior days’ transaction data.

Given the number of trailing days  and a client’s total daily expenditures for a period of  days, determine the number of times the client will receive a notification over all  days.


On the first three days, they just collect spending data. At day , trailing expenditures are . The median is  and the day’s expenditure is . Because , there will be a notice. The next day, trailing expenditures are  and the expenditures are . This is less than  so no notice will be sent. Over the period, there was one notice sent.

Note: The median of a list of numbers can be found by first sorting the numbers ascending. If there is an odd number of values, the middle one is picked. If there is an even number of values, the median is then defined to be the average of the two middle values. (Wikipedia)

Function Description

Complete the function activityNotifications in the editor below.

activityNotifications has the following parameter(s):

  • int expenditure[n]: daily expenditures
  • int d: the lookback days for median spending


  • int: the number of notices sent

Input Format

The first line contains two space-separated integers  and , the number of days of transaction data, and the number of trailing days’ data used to calculate median spending respectively.
The second line contains  space-separated non-negative integers where each integer  denotes .


Output Format

Sample Input 0

STDIN               Function
-----               --------
9 5                 expenditure[] size n =9, d = 5
2 3 4 2 3 6 8 4 5   expenditure = [2, 3, 4, 2, 3, 6, 8, 4, 5]

Sample Output 0


Explanation 0

Determine the total number of  the client receives over a period of  days. For the first five days, the customer receives no notifications because the bank has insufficient transaction data: .

On the sixth day, the bank has  days of prior transaction data, , and  dollars. The client spends  dollars, which triggers a notification because : .

On the seventh day, the bank has  days of prior transaction data, , and  dollars. The client spends  dollars, which triggers a notification because : .

On the eighth day, the bank has  days of prior transaction data, , and  dollars. The client spends  dollars, which does not trigger a notification because : .

On the ninth day, the bank has  days of prior transaction data, , and a transaction median of  dollars. The client spends  dollars, which does not trigger a notification because : .

Sample Input 1

5 4
1 2 3 4 4

Sample Output 1


There are  days of data required so the first day a notice might go out is day . Our trailing expenditures are  with a median of  The client spends  which is less than  so no notification is sent.

Fraudulent Activity Notifications – Hacker Rank Solution
import java.lang.reflect.Array;
import java.util.*;

public class Main implements Runnable {

    int[] cnt;

    int med(int d) {
        int[] a = Arrays.copyOf(cnt, cnt.length);
        int r = d / 2;
        if (d % 2 == 1) {
        int res = 0;
        boolean odd = d % 2 == 1;
        for (int k = 0; k <= 200; k++) {
            while (r > 0 && a[k] > 0) {
            if (r == 0) {
                res += k;
                if (d % 2 == 0) {
                    if (a[k] > 0) {
                        return 2 * k;
                } else {
        return res * (odd ? 2 : 1);

    void solve() throws IOException {
        int n = nextInt();
        int d = nextInt();
        cnt = new int[201];
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextInt();
        for (int i = 0; i < d; i++) {
        int res = 0;
        for (int i = d; i < n; i++) {
            int m = med(d);
            if (a[i] >= m) {
            cnt[a[i - d]]--;


    BufferedReader br;
    StringTokenizer st;
    PrintWriter out;

    public void run() {
        try {
            br = new BufferedReader(new InputStreamReader(;
            out = new PrintWriter(System.out);

        } catch (Exception e) {

    String next() throws IOException {
        while (st == null || !st.hasMoreTokens()) {
            String s = br.readLine();
            if (s == null)
                return null;
            st = new StringTokenizer(s);
        return st.nextToken();

    double nextDouble() throws IOException {
        return Double.parseDouble(next());

    int nextInt() throws IOException {
        return Integer.parseInt(next());

    long nextLong() throws IOException {
        return Long.parseLong(next());

    public static void main(String[] args) {
        new Thread(new Main()).start();

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