BillDesk Senior Software Engineer Interview Questions and Answers

DP questions 1D DP and Array question

Q1. Java questions and technical questions from previous experience
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Q1. Behavioural questions and standard HR questions
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Q2. Why looking for job switch
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Q1. Minimum number of platforms required for train station
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Q2. Longest Palindromic substring
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Q1. Sort the elements of an unsorted array
Ans. 
Use any sorting algorithm to sort the elements of an unsorted array.
• Choose an appropriate sorting algorithm based on the size of the array and the type of elements.

• Common sorting algorithms include bubble sort, insertion sort, selection sort, merge sort, quick sort, and heap sort.

• Implement the chosen algorithm in the programming language of your choice.

• Test the sorting function with various input arrays to ensure corre...read more
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Q2. Minimum energy required to cross all the hurdles without loosing life. If any point energy becomes 0 game over. Input: [-2,-3,3,1,5]
Ans. 
Find minimum energy required to cross all hurdles without losing life.
• Calculate cumulative sum of energy required to cross each hurdle.

• Find the minimum cumulative sum and add 1 to it.

• If the minimum cumulative sum is negative, return its absolute value + 1.

• This is the minimum energy required to cross all hurdles without losing life.
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Q1. Find edge score of the nodes in a directed graph
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Edge score of nodes in a directed graph
• Edge score is a measure of the importance of a node in a graph

• It is calculated by counting the number of edges that point to or from a node

• Nodes with higher edge scores are considered more important

• Edge score can be calculated using algorithms like PageRank or HITS
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Q1. Rotten oranges after every second in 2D matrix
Ans. 
Simulate rotting of oranges in a 2D matrix every second.
• Create a queue to store the coordinates of fresh oranges

• Iterate through the matrix and add the coordinates of fresh oranges to the queue

• Simulate the rotting process by iterating through the queue and rotting adjacent fresh oranges

• Keep track of the time taken for all oranges to rot

• Return -1 if there are any fresh oranges left after the simulation
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Q2. Java and Spring concepts, HTTP, HTTPS, OSI layers
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Q3. DB design for air ticket booking system
Ans. 
DB design for air ticket booking system
• Create tables for flights, passengers, bookings, and payments

• Use foreign keys to establish relationships between tables

• Include fields for flight details, passenger information, and payment details

• Consider implementing a caching mechanism for frequently accessed data
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Q1. LC 410: Split Array Largest Sum
Ans. 
Split an array into 'm' subarrays to minimize the largest sum among them.
• Use binary search to find the minimum largest sum possible.

• Define a helper function to check if a target sum can be achieved with 'm' splits.

• Example: For array [7, 2, 5, 10, 8] and m=2, the optimal split is [7, 2, 5] and [10, 8] with largest sum 15.
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Q2. Intro was asked
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Implement thread safe load balancer.
focus on input validations and cover all corner cases in tests

Q1. Low Level Design: How to do rate limiting for a platform serving 100K requests per second.
Ans. 
Implement rate limiting for a platform serving 100K requests per second.
• Use a token bucket algorithm to limit the rate of incoming requests.

• Set a maximum number of tokens in the bucket to control the rate.

• Refill the bucket at a constant rate to allow bursts of requests.

• Track the timestamp of the last request to enforce the rate limit.

• Consider using a distributed rate limiting system for scalability.

• Monitor and adjust t...read more
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