Nextdoor Interview Questions

Nextdoor is one of the most well-known neighborhood-focused social networking platforms, dedicated to fostering local community connections and facilitating communication between neighbors. As a data-driven enterprise, it leverages robust software engineering, data science, and machine learning to enhance user experience and services.

Interviews at Nextdoor prioritize gathering information about your past experience (i.e., previous job achievements, philosophy, etc.) and asking multi-faceted technical questions.

To help you prepare effectively for a Nextdoor interview, this guide provides a wide range of practice interview questions to gauge your proficiency in these critical areas.

At Nextdoor, SQL is especially important because the platform uses large-scale data to improve user experience and make decisions.

Nextdoor’s engineering team uses PostgreSQL for the majority of their storage needs, including for analytics purposes. As such, the company heavily emphasizes SQL questions throughout the interview process.

1. How would you write a query to find neighborhoods with no users?

Given a users table with demographic information and the neighborhood they live in and a neighborhoods table, write a query that returns all neighborhoods that have 0 users.

2. How would you write a query to get the last transaction for each day?

Given a table of bank transactions with columns id, transaction_value, and created_at (representing the date and time for each transaction), write a query to find the last transaction for each day.

The output should include the id of the transaction, datetime of the transaction, and the transaction amount. Order the transactions by datetime.

3. Using multiple queries, find transaction information to answer the following questions.

Given an annual_payments table, write SQL queries for the following:

1. How many total transactions are in this table?
2. How many different users made transactions?
3. How many transactions listed as "paid" have an amount greater or equal to 100?
4. Which product made the highest revenue? Use only transactions with a "paid" status.

Try the SQL learning path and a full list of SQL questions and solutions in our interview questions database for more practice.

Machine learning forms the backbone of many of Nextdoor’s critical functions, from personalized content recommendation to fraud detection. It allows the platform to learn from past data and predict future outcomes for proactive decision-making. These questions appear frequently in interviews with data scientists and machine learning engineers.

4. How would you design a system to detect and prevent the sale of a banned item?

You’re designing a marketplace for your website where selling firearms is prohibited. You need to create a system that automatically detects if a listing on the marketplace is selling a gun. How would you approach this task?

5. How would you build a model to optimize keyword bidding using a given dataset?

You’re working on keyword bidding optimization. Given a dataset with two columns, one containing the keywords being bid against and the other containing the price of those keywords, how would you build a model to bid on a new unseen keyword?

6. Describe some functional and non-functional requirements for a machine learning product that predicts usage rate.

You work on an AI team and are tasked with creating a product to predict the number of daily transit riders of the New York City Subway at a given hour. You’ll receive hourly data from your client’s database to use as training data for supplementing your current AI’s working dataset. Predictions should be delivered on an hourly basis.

To start off your project, what are the product’s requirements?

To prepare for more complex machine learning interview questions, use the machine learning learning path.

In tech, problems can arise in the most unpredictable ways, with a simple edge case shutting down production. In the interview process, case study questions, which are modeled after real-world problems, allow interviews to assess whether candidates can create quick and practical solutions that are highly valued in the workplace.

7. How would you set up an A/B test for multiple changes in a sign-up funnel?

A team wants to A/B test various changes in a sign-up funnel. For example, a button on a page is currently red and located at the top.

The team wants to see if changing the button’s color to blue and/or moving it to the bottom will increase click-through rates. How would you set up this test?

8. How would you generate a daily report to evaluate campaign performance?

Given a schema representing advertisement campaigns and impressions, generate a daily report showing how each campaign delivered during the first 7 days. Round your output to 4 decimal places.

How would you use this data to evaluate campaign delivery and determine which promos need more attention?

9. Analyze the distribution of daily messages sent between two users.

We have a table that represents the total number of messages sent between two users by date on Messenger.

• What insights could be derived from this table?
• What might the distribution of the number of conversations created by each user per day look like?
• Write a query to get the distribution of the number of conversations created by each user by day in the year 2020.

For case studies, you can utilize resources like the product metrics and data analytics learning paths to further develop your approach to these questions.

At Nextdoor, having a strong foundation for data structures, algorithms, and proficiency in languages like Python or R is indispensable for any technical role. This section explores different coding questions to assess your ability to develop efficient, scalable solutions for complex problems.

10. How would you write a program to calculate the number of business days between two dates?

Example input:

date1 = 2021-01-31
date2 = 2021-02-18

11. Write a function to remove stop words from a string.

Given a list of stop words, write a function stopwords_stripped that takes a string and returns a string stripped of the stop words with all lowercase characters.

Example input:

stopwords = [
    'I',
    'as',
    'to',
    'you',
    'your',
    'but',
    'be',
    'a',
]

paragraph = 'I want to figure out how I can be a better data scientist'

12. How would you write a function to return the top N frequent words in a string?

Given a paragraph string and an integer N, write a function n_frequent_words that returns the top N frequent words in the posting and the frequencies for each word.

What is the function’s run-time?

Example input:

posting = """
Herbal sauna uses the healing properties of herbs in combination with distilled water.
The water evaporates and distributes the effect of the herbs throughout the room.
A visit to the herbal sauna can cause real miracles, especially for colds.
"""
n = 3

To practice Algorithms interview questions, try the Python learning path and the Algorithms questions in our database.

Behavioral interview questions are very reflective of a candidate’s soft skills, character, and fit for the company culture. At Nextdoor, an employee is expected to not only be technically proficient, but also capable of contributing to a dynamic and collaborative workplace.

This includes dealing with tight deadlines, managing conflicts, and contributing positively to team dynamics and community building. The following questions are designed to uncover your behavioral tendencies in such scenarios and assess how well they align with Nextdoor’s work culture and values.

13. How have you used your skills to help build stronger, safer, and happier communities?

This question directly pertains to Nextdoor’s mission. When answering, highlight experiences where you’ve utilized data analysis, machine learning, or other relevant skills to positively impact a community. It could be a feature you helped develop, a campaign you influenced, or a policy you shaped that had a direct positive effect on users or community members.

14. Tell us about a time when you had to work on a tight deadline.

Nextdoor, like any tech company, operates in a fast-paced environment. Describe a specific incident where you efficiently managed your time, resources, and stress levels to deliver a project on time. In your answer, focus on your problem-solving abilities, how you prioritized tasks, and your capacity to remain calm and focused under pressure.

15. How do you prioritize projects under pressure?

This question aims to assess your decision-making and project management skills. In addition to outlining your strategy based on factors like urgency, impact, effort, etc., use specific examples to demonstrate how you’ve effectively used this strategy in a past role.

To ace your interviews at Nextdoor, brush up on your knowledge using our SQL Learning Path and practice for technical interviews with our curated pool of interview questions, freshly gathered from companies around the world.