Opendoor Senior Software Engineer Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

Total of 8 questions:

4 MCQ(oops and expected output type questions) + other 2 were coding questions, out of which one is some class implementation question.

Q1. 
Count Subarrays with Sum Divisible by K
Given an array ARR and an integer K, your task is to count all subarrays whose sum is divisible by the given integer K.
Input:
The first line of input contains an...read more
Ans. 
Count subarrays with sum divisible by K in an array.
• Iterate through the array and keep track of the running sum modulo K.

• Use a hashmap to store the frequency of remainders.

• For each prefix sum, check how many previous prefix sums have the same remainder.

• Return the total count of subarrays with sum divisible by K.
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Round duration - 60 minutes
Round difficulty - Easy

This round was with the USA team, the panel consisted of 2 members. It took place at around 9 PM IST. The interviewer's focus was on approach.

Q1. 
Sort an Array in Wave Form
You are given an unsorted array ARR. Your task is to sort it so that it forms a wave-like array.
Input:
The first line contains an integer 'T', the number of test cases.
For ea...read more
Ans. 
Sort an array in a wave-like pattern where each element is greater than or equal to its adjacent elements.
• Iterate through the array and swap elements at even indices with their adjacent odd indices to form a wave pattern.

• There can be multiple valid wave arrays, so any valid wave array is acceptable.

• Ensure the first element is greater than or equal to the second element to start the wave pattern.
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Q2. 
Convert a Number to Words
Given an integer number num, your task is to convert 'num' into its corresponding word representation.
Input:
The first line of input contains an integer ‘T’ denoting the number o...read more
Ans. 
Convert a given integer number into its corresponding word representation.
• Implement a function that takes an integer as input and returns the word representation of that number.

• Break down the number into its individual digits and convert each digit into its word form.

• Handle special cases like numbers between 10 and 19, and multiples of 10.

• Combine the word forms of individual digits to form the final word representation
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Round duration - 40 minutes
Round difficulty - Easy

It was a managerial round. The position of the person taking the interview was of a technical architect. As was informed by the recruiter, previously he was a technical architect at Amazon.

Q1. How does Facebook store comments in its database?
Ans. 
Facebook stores comments in its database using a combination of relational and non-relational databases.
• Comments are typically stored in a relational database like MySQL for structured data storage.

• For scalability and performance, Facebook may also use a NoSQL database like Cassandra or HBase for storing comments in a denormalized format.

• Metadata related to comments such as likes, timestamps, and user information may b...read more
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