Backend Engineer Online Test

You are working on a large-scale, distributed, and fault-tolerant message processing system designed to handle high throughput and low latency requirements. The system is based on the publish-subscribe pattern and uses multiple brokers to distribute messages across various topics and partitions. In this architecture, both publishers and subscribers are considered clients. The brokers are responsible for replicating messages among themselves to ensure fault tolerance and data durability.

A client reports successfully publishing a message on a specific topic. However, one of the subscribers has not received the message. To investigate the issue, you have gathered detailed logs and system design data, as shown below:

Based on the information provided, which of the following is the most likely reason for the issue?

A: The message was not published on the topic
B: Client C is not subscribed to the correct topic
C: There is a replication lag between brokers B1 and B2
D: Client C is consuming from the wrong broker
E: The message processing system failed to acknowledge the message

A backend service is experiencing intermittent latency spikes while processing incoming requests. The service is deployed in a multi-node environment with a load balancer in front. You suspect that the issue might be related to resource contention. You collect the following performance metrics from the affected nodes during a spike:

Which of the following is the most probable cause of the latency spikes?
A: High memory usage on the affected nodes.
B: Disk I/O bottlenecks on the affected nodes.
C: Insufficient CPU resources on the affected nodes.
D: Uneven distribution of incoming requests by the load balancer.
E: Network latency between the load balancer and the backend nodes.

What does the following pseudo code print?

Here are three pseudocodes for calculating the Nth Fibonacci number. Which of the following statements about these codes are true?

A: Time complexity/efficiency of CODE 1, CODE 2, CODE 3 is the same.
B: CODE 2 is more space-efficient than CODE 3.
C: CODE 3 is more space-efficient than CODE 2.
D: CODE 2 is more time-efficient than CODE 1.
E: CODE 3 is more time-efficient than CODE 1.

Go through the following faulty palindrome detection pseudocode and test cases. For which of the test cases would the code return true?

Testcases
A: a
B: aba
C: aaa
D: aac

A new popular app tracks the activities performed by its users and grants them rewards based on each individual's total activities performed in a year. This data is maintained in a database table (activitesinfo), with the following columns: userid, totalactivities, reward. This year, due to fundraising activity, the company has decided to further reward its users by enhancing the reward as per the following formula: If reward < = 4000, increase it by 2%, If 4000 < reward <= 8000, increase it by 4%, If reward > 8000, increase it by 6%.
The tech team has written three different scripts to calculate increment for each slab, each script is to run as a separate transaction. Here are the three scripts:

Script 1:
For users with reward <= 4000, set reward = reward * 1.02

Script 2:
For users with reward > 4000 and reward <= 8000, set reward = reward * 1.04

Script 3:
For users with reward > 8000, set reward = reward * 1.06

Each script is to be executed separately. Which of the following options will update the rewards as expected:

A: Execute Script 1 followed by Script 2 followed by Script 3
B: Execute Script 2 followed by Script 3; Script 1 running concurrently throughout
C: Execute Script 3 followed by Script 2; Script 1 running concurrently throughout
D: Execute Script 3 followed by Script 2 followed by Script 1
E: Execute Script 2 followed by Script 3 followed by Script 1

We want to register students for the next semester. All students have a receipt which shows the amount pending for the previous semester. A positive amount (or zero) represents that the student has paid extra fees, and a negative amount represents that they have pending fees to be paid. The students are in a queue for the registration. We want to arrange the students in a way such that the students who have a positive amount on the receipt get registered first as compared to the students who have a negative amount. We are given a queue in the form of an array containing the pending amount.

For example, if the initial queue is [20, 70, -40, 30, -10], then the final queue will be [20, 70, 30, -40, -10]. Note that the sequence of students should not be changed while arranging them unless required to meet the condition.

⚠️⚠️⚠️ Note:
- The first line of the input is the length of the array. The second line contains all the elements of the array.
- The input is already parsed into an array of "strings" and passed to a function. You will need to convert string to integer/number type inside the function.
- You need to "print" the final result (not return it) to pass the test cases.

For the example discussed above, the input will be:
5
20 70 -40 30 -10

Your code needs to print the following to the standard output:
20 70 30 -40 -10

A startup company E-Motors is building driverless automated cars. The car contains a sensor that checks the road quality for the next N meters to decide the optimal speed at which the cars should move. We are given recorded data by the sensor in the form of an array, where each element of the array is the rating given to 1 meter of the road in sequence. 

The rating given by the sensor is from 1 to 100, where 100 represents the road with the best condition, and any rating above 60 is optimal. Find the longest stretch of road in meters that is categorized as optimal by the sensor.

The input is an array of "strings" which needs to be converted from string to integer/number inside the function.

A manager hires a staff member to keep a record of the number of men, women, and children visiting the museum daily. The staff will note W if any women visit, M for men, and C for children. You need to write code that takes the string that represents the visits and prints the count of men, woman and children. The sequencing should be in decreasing order. 

Example:

Input:
WWMMWWCCC

Expected Output: 
4W3C2M

Explanation: 
‘W’ has the highest count, then ‘C’, then ‘M’. 

⚠️⚠️⚠️ Note:
- The input is already parsed and passed to a function.
- You need to "print" the final result (not return it) to pass the test cases.
- If the input is- “MMW”, then the expected output is "2M1W" since there is no ‘C’.
- If any of them have the same count, the output should follow this order - M, W, C.