Prepare for and practice interview questions from Argonne National Laboratory across topics like Algorithms, Python, Statistics and more.

Argonne National Laboratory Interview Questions

Argonne National Laboratory Interview Guides

Machine Learning

What are the logistic and softmax functions? What is the difference between the two?

Softmax vs Logistic

What are some reasons why measuring bias would be important in building this particular model

Food Delivery Times

How would you evaluate whether a decision tree is the right model and assess its performance before and after deployment

Decision Tree Evaluation

How to model merchant acquisition in a new market?

Merchant Acquisition

Explain the key differences between classification models and regression models

Classification and Regression

A/B Testing

Button AB Test

How would you make a control group and test group to account for network effects

Network Experiment Design

How would you analyze the effectiveness of this new feature?

Green Dot

How would you design a two-week A/B test to determine whether a pricing increase is a good business decision

Testing Price Increase

Precisely ascertain whether the outcomes of an A/B test, executed to assess the impact of a landing page redesign, exhibit statistical significance.

Statistically Significant Test

Data Structures & Algorithms

Given two sorted lists, write a function to merge them into one sorted list.

Merge Sorted Lists

Find the missing integer from a array of consequtive integers

Find the Missing Number

Write a function one_element_removed that returns the integer removed from list Y in O(1) space and O(n) time without using set

One Element Removed

Transform a dataframe containing a list of user IDs and their full names into one that contains only the user ids and the first name of each user.

First Names Only

Given an array and a target integer, write a function that returns the indices of two integers in the array that add up to the target integer.

Target Indices

Behavioral

Strategically resolving misaligned expectations with stakeholders for a successful project outcome

Stakeholder Communication

How would you answer when an Interviewer asks why you applied to their company?

Why Do You Want to Work With Us

What do you tell an interviewer when they ask you what your strengths and weaknesses are?

Your Strengths and Weaknesses

Business Case

Diagnose why the pricing algorithm is under-pricing a consumer product

Underpricing Algorithm

How would you create a policy for refunds with regards to balancing customer sentiment and goodwill versus revenue tradeoffs?

Food Delivery Refund Policy

Given two sorted lists, write a function to merge them into one sorted list.

Bonus: What’s the time complexity?

Example:

Input:

<pre tabindex="0" class="chroma"><code>list1 = [1,2,5]
list2 = [2,4,6]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def merge_list(list1,list2) -&gt; [1,2,2,4,5,6]
</code></pre>

You have two sorted lists, one with m elements and one with n elements. What would be the time complexity of merging the two lists via merge sort?

You have two sorted lists, one with m elements and one with n elements. What would be the time complexity of merging the two lists via merge sort? 

Merging Lists Complexity

A team wants to A/B test multiple different changes through a sign-up funnel.

For example, on a page, a button is currently red and at the top of the page. They want to see if changing a button from red to blue and/or from the top of the page to the bottom of the page will increase click-through.

How would you set up this test?

Your team wants to run an AB test on the color (red or blue) and position (top/bottom of the page) of a button that links to a promotion.

How many different variants of the test should you run to see the effect that a red button has on the bottom of the page, if currently the button is blue and on the top of the page.

Your team wants to run an AB test on the color (red or blue) and position (top/bottom of the page) of a button that links to a promotion.

How many different variants of the test should you run to see the effect that a red button has on the bottom of the page, if currently the button is blue and on the top of the page.

A/B Test Variants

You have an array of integers, <code>nums</code> of length <code>n</code> spanning <code>0</code> to <code>n</code> with one missing. Write a function <code>missing_number</code> that returns the missing number in the array.

Note: Complexity of \(O(n)\) required.

Example:

Input:

<pre tabindex="0" class="chroma"><code>nums = [0,1,2,4,5] 
missing_number(nums) -&gt; 3
</code></pre>

Over budget on a project is defined when the salaries, prorated to the day, exceed the budget of the project.

For example, if Alice and Bob both combined income make 200K and work on a project of a budget of 50K that takes half a year, then the project is over budget given 0.5 * 200K = 100K &gt; 50K.

Write a query to forecast the budget for all projects and return a label of <code>&#34;overbudget&#34;</code> if it is over budget and <code>&#34;within budget&#34;</code> otherwise.

Note: Assume that employees only work on one project at a time.

Example:

Input:

<code>employees</code> table

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>first_name</code></td>
<td>VARCHAR</td>
</tr>

<tr>
<td><code>last_name</code></td>
<td>VARCHAR</td>
</tr>

<tr>
<td><code>salary</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>department_id</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>
<code>projects</code> table

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>title</code></td>
<td>VARCHAR</td>
</tr>

<tr>
<td><code>state_date</code></td>
<td>DATETIME</td>
</tr>

<tr>
<td><code>end_date</code></td>
<td>DATETIME</td>
</tr>

<tr>
<td><code>budget</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>
departments table

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>name</code></td>
<td>VARCHAR</td>
</tr>
</tbody>
</table>
<code>employee_projects</code> table

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>project_id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>employee_id</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>
Output:

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>title</code></td>
<td>VARCHAR</td>
</tr>

<tr>
<td><code>project_forecast</code></td>
<td>VARCHAR</td>
</tr>
</tbody>
</table>

Write a query to forecast each project's budget and label it overbudget or within budget

Over-Budget Projects

Let’s say you want to test the close friends feature on Instagram Stories.

How would you make a control group and test group to account for network effects?

What could be a potential risk when Facebook segments the metrics of the user interface change by market or demographic groups?

What could be a potential risk when Facebook segments the metrics of the user interface change by market or demographic groups?

Network Experiment Design I

What is the primary metric that Facebook should monitor if it decides to make the user interface of its posting feature more like Instagram's?

What is the primary metric that Facebook should monitor if it decides to make the user interface of its posting feature more like Instagram's?

Network Experiment Design II

If Facebook changes its user interface to mimic Instagram's, which adverse effect should they anticipate and monitor?

If Facebook changes its user interface to mimic Instagram's, which adverse effect should they anticipate and monitor?

Network Experiment Design III

There are two lists, <code>list X</code> and <code>list Y</code>. Both lists contain integers from <code>-1000</code> to <code>1000</code> and are identical to each other except that one integer is removed in <code>list Y</code> that exists in <code>list X</code>.

Write a function <code>one_element_removed</code> that takes in both lists and returns the integer that was removed in \(O(1)\) space and \(O(n)\) time without using the python set function.

Example:

Input:

<pre tabindex="0" class="chroma"><code>list_x = [1,2,3,4,5]
list_y = [1,2,4,5]

one_element_removed(list_x, list_y) -&gt; 3
</code></pre>

Which of the following methods would be the most efficient way of identifying what element is not included in two lists of integers that differ by a single element being removed?

For example, if the lists are <code>[1,2,3,4,5]</code> and <code>[1,2,4,5]</code>, the function should return <code>3</code>

Which of the following methods would be the most efficient way of identifying what element is not included in two lists of integers that differ by a single element being removed? 

For example, if the lists are `[1,2,3,4,5]` and `[1,2,4,5]`, the function should return `3`

Efficiently Identifying Missing Integer

Let’s say you’re a Product Data Scientist at Instagram. How would you measure the success of the Instagram TV product?

What is the primary goal of Instagram TV as a product feature?

What is the primary goal of Instagram TV as a product feature?

Instagram TV Success

How would you measure the success of the Instagram TV product

Product Sense & Metrics

How would you handle the data preparation for building a machine learning model using imbalanced data?

Addressing imbalanced data in machine learning through carefully prepared techniques.

Data Preparation for Imbalanced Data

You are a data scientist at YouTube focused on creators.

A PM comes to you worried that amateur video creators could do well before but now it seems like only “superstars” do well.

What data points and metrics would you look at to decide if this is true or not?

What data points and metrics would you look at to decide if amateur creators are doing worse and only superstars do well

Amateur Performance

Let’s say we’re working on a new feature for LinkedIn chat. We want to implement a green dot to show an “active user” but given engineering constraints, we can’t AB test it before release.

How would you analyze the effectiveness of this new feature?

Given a list of integers, identify all the duplicate values in the list. Assume that the list can contain both positive and negative numbers, and the order of the list does not matter. A number is considered a duplicate if it appears more than once in the list. Return a list of the duplicate numbers.

Example 1:

Input:

<pre tabindex="0" class="chroma"><code>nums = [1, 2, 3, 1, 2, 3]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>find_duplicates(nums) -&gt; [1, 2, 3]
</code></pre>

The numbers 1, 2, and 3 all appear more than once in the list, so they are considered duplicates.

Example 2:

Input:

<pre tabindex="0" class="chroma"><code>nums = [1, -1, 2, 3, 3, -1]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>find_duplicates(nums) -&gt; [-1, 3]
</code></pre>

The numbers -1 and 3 both appear more than once in the list, so they are considered duplicates. Note that the order of the output does not matter.

Example 3:

Input:

<pre tabindex="0" class="chroma"><code>nums = [1, 2, 3, 4, 5]
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>find_duplicates(nums) -&gt; []
</code></pre>

None of the numbers in the list appear more than once, so there are no duplicates.

This problem involves identifying duplicate numbers in a list of integers. The function should return a list of the duplicate numbers.

Find Duplicate Numbers in a List

Given an array and a target integer, write a function <code>sum_pair_indices</code> that returns the indices of two integers in the array that add up to the target integer. If not found, just return an empty list.

Note: Can you do it on \(O(n)\) time?

Note: Even though there could be many solutions, only one needs to be returned.

Example 1:

Input:

<pre tabindex="0" class="chroma"><code>array = [1 2 3 4] 
target = 5 
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def sum_pair_indices(array, target) -&gt; [0 3] or [1 2]
</code></pre>

Example 2:

Input:

<pre tabindex="0" class="chroma"><code>array = [3]
target = 6 
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>Do NOT return [0 0] as you can&#39;t use an index twice.
</code></pre>

Let’s say you’re a data scientist at LinkedIn where you’re working on a product that sends qualified job candidates to companies. The team has launched a new feature that allows candidates to message hiring managers at companies directly during the interview process to get updates on their status.

Due to engineering constraints, the company can’t AB test the feature before launching it.

How would you analyze how the feature is performing?

How would you analyze the performance of a new LinkedIn feature that lets candidates message hiring managers during the interview process

Recruiting Leads

Analytics

Let’s say that you work at a B2B SAAS company that’s interested in testing the pricing of different levels of subscriptions.

Your project manager comes to you and asks you to run a two-week-long A/B test to test an increase in pricing.

How would you approach designing this test? How would you determine whether the increase in pricing is a good business decision?

Design a database to represent a Tinder style dating app. 

What does the schema look like and what are some optimizations that you think we might need?

Let’s say you are making a swiping app, similar to Tinder.

What would be the most efficient way (in terms of retrieval time) to store which users have swiped on each other on a database backend?

Let's say you are making a swiping app, similar to Tinder.

What would be the most efficient way (in terms of retrieval time) to store which users have swiped on each other on a database backend?

Swipes Database Design

Design a database schema for a Tinder-style dating app and discuss needed optimizations

Swiping App Design

Data Modeling

Let’s say that you work as a data scientist at a food delivery company.

You are tasked with building a model to predict food preparation times at a restaurant from the time when a customer sends in the order to when the meal is ready for the driver to pick up.

What are some reasons why measuring bias would be important in building this particular model?

You are required to extract a specific word <code>target_word</code> from an encrypted document. Fortunately, you have the basic information needed to decrypt that document.

The equation used to encrypt the document is as follows:

\[E_n(x) = (I(\mathsf{s}) + n) \mod 26 \]

Where:

<ul>
<li>\(\mathsf{s}\) is a letter</li>
<li>\(I(x) \) is the number representing the position of the letter in the alphabet (1 for <code>A</code>, 2 for <code>B</code>, etc.)</li>
<li>\(n \) is an arbitrary integer.</li>
<li>\(E_n(x) \) is the encrypted letter.</li>
</ul>

Return the number of occurrences of <code>target_word</code> in the document after decryption.

Note: The document only has upper case letters and spaces.

Example:

Input:

<pre tabindex="0" class="chroma"><code>encrypted_document = &#39;WKH TXLFN EURZQ IRA MXPSV RYHU WKH ODCB GRJ&#39;
n = 3
target_word = &#39;BROWN&#39;
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>extract_word(encrypted_document,n,target_word) -&gt; 1
</code></pre>

Explanation:

After decrypting the document, you will have :

<pre tabindex="0" class="chroma"><code>THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
</code></pre>

In which the <code>target_word</code> (BROWN) appears only once.

Return the number of occurrences of `target_word` in the decrypted document

Words in Encrypted String

What are the key differences between classification models and regression models?

What is the MOST important difference between regression and classification models?

What is the MOST important difference between regression and classification models?

Classification vs Regression

What are the logistic and softmax functions? What is the difference between the two?

What makes them useful for use in logistic regression?

In logistic regression, how is the predicted class determined based on the logistic function?

In logistic regression, how is the predicted class determined based on the logistic function?

Softmax vs Logistic II

What is the key characteristic of the logistic function that makes it useful for mapping continuous values to a probability?

What is the key characteristic of the logistic function that makes it useful for mapping continuous values to a probability?

Softmax vs Logistic I

You’re given a dataframe containing a list of user IDs and their full names (e.g. ‘James Emerson’).

Transform this dataframe into a dataframe that contains the user ids and only the first name of each user.

Example:

Input:

<table>
<thead>
<tr>
<th>user_id</th>
<th>name</th>
</tr>
</thead>

<tbody>
<tr>
<td>1034</td>
<td>James Emerson</td>
</tr>

<tr>
<td>9430</td>
<td>Fiona Woodward</td>
</tr>

<tr>
<td>7281</td>
<td>Alvin Gross</td>
</tr>

<tr>
<td>5264</td>
<td>Deborah Handler</td>
</tr>

<tr>
<td>8995</td>
<td>Leah Xue</td>
</tr>
</tbody>
</table>
Output:

<table>
<thead>
<tr>
<th>user_id</th>
<th>name</th>
</tr>
</thead>

<tbody>
<tr>
<td>1034</td>
<td>James</td>
</tr>

<tr>
<td>9430</td>
<td>Fiona</td>
</tr>

<tr>
<td>7281</td>
<td>Alvin</td>
</tr>

<tr>
<td>5264</td>
<td>Deborah</td>
</tr>

<tr>
<td>8995</td>
<td>Leah</td>
</tr>
</tbody>
</table>

Let’s say you have analytics data stored in a data lake. An analyst tells you they need hourly, daily, and weekly active user data for a dashboard that refreshes every hour.

How would you build this data pipeline?

Design a data pipeline to compute hourly, daily, and weekly active user metrics from a data lake for an hourly-refreshing dashboard

Data Pipelines and Aggregation

Data Pipelines

When an interviewer asks you a question along the lines of:

<ul>
<li>Why did you apply to our company?</li>
<li>What are you looking for in your next job?</li>
<li>What makes you a good fit for our company?</li>
</ul>

How should you respond?

When asked 'What are you looking for in your next job?' in an interview, how can you tie the company's employee benefits into your response?

When asked 'What are you looking for in your next job?' in an interview, how can you tie the company's employee benefits into your response?

Why Do You Want to Work With Us I

How can company values be used effectively in an interview when asked 'What makes you a good fit for our company?'

How can company values be used effectively in an interview when asked 'What makes you a good fit for our company?'

Why Do You Want to Work With Us II

When responding to the question 'Why did you apply to our company?' during an interview, what aspect should you highlight?

When responding to the question 'Why did you apply to our company?' during an interview, what aspect should you highlight?

Why Do You Want to Work With Us III

You work on an artificial intelligence team at ABC Neural Inc. Your client, the New York City Transit Authority, provides an hourly feed of subway ridership data (entries and exits) for the NYC Subway system. Your task is to predict the number of riders each hour for each subway station.

Design and outline a solution (both functional and non-functional requirements) that takes the hourly ridership data as input and delivers predictions of hourly ridership back to the client. Predictions must be consistently updated as new data arrives, and the end product will be integrated into the client’s internal systems.

Design a machine learning solution to predict hourly subway ridership for each NYC subway station using hourly entry and exit data

Subway Machine Learning Model

Let’s say we’ve built a churn prediction model for a subscription service using user behavior data from the past 12 months, and now we want to deploy it to production and also apply it to a new user segment that wasn’t in our original training data.

How would you approach preparing the model for deployment and ensuring it generalizes well to the new dataset?

How would you get a model ready for production use and adaptation to new datasets?

Model Deployment Preparation

ML Ops

Let’s say that you’re a data scientist working for Facebook.

You’ve been asked to generate a machine learning model that can map the legal first name of a person to likely nicknames they might have.

How do you go about designing this model?

Mapping Nicknames

When an interviewer asks a question along the lines of:

<ul>
<li>What would your current manager say about you? What constructive criticisms might he give?</li>
<li>What are your three biggest strengths and weaknesses you have identified in yourself?</li>
</ul>

How would you respond?

When asked about your strengths in an interview, what is an effective way to respond?

When asked about your strengths in an interview, what is an effective way to respond?

Your Strengths and Weaknesses I

Which of the following is an acceptable strategy when discussing weaknesses in an interview?

Which of the following is an acceptable strategy when discussing weaknesses in an interview?

Your Strengths and Weaknesses II

Find all sets of 3 indexes of an array so that the three indexed elements add up to 0.

Note: You may assume the input array is sorted in ascending order.

<h3>Example</h3>

For example, if the input array is:

<pre tabindex="0" class="chroma"><code>array = [-2, -1, 1, 1, 3]
</code></pre>

The result should be:

<pre tabindex="0" class="chroma"><code>result = [{0,1,2}, {2,3,4}]
</code></pre>

Find all sets of 3 indexes whose elements add up to 0.

Three Indexes Adding Zero

You are given a graph, which is implemented as a 2D array. Each cell in the array represents a node and the value in the cell represents the cost to traverse to that node. You are also given a start node and an end node. Your task is to implement a function that finds the shortest path from the start node to the end node using any shortest path algorithm.

Example 1:

Input:

<pre tabindex="0" class="chroma"><code>graph = [[0, 4, 0, 0, 0, 0, 0, 8, 0],
 [4, 0, 8, 0, 0, 0, 0, 11, 0],
 [0, 8, 0, 7, 0, 4, 0, 0, 2],
 [0, 0, 7, 0, 9, 14, 0, 0, 0],
 [0, 0, 0, 9, 0, 10, 0, 0, 0],
 [0, 0, 4, 14, 10, 0, 2, 0, 0],
 [0, 0, 0, 0, 0, 2, 0, 1, 6],
 [8, 11, 0, 0, 0, 0, 1, 0, 7],
 [0, 0, 2, 0, 0, 0, 6, 7, 0]]
start = 0
end = 4
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>shortest_path(graph, start, end) -&gt; [0, 1, 2, 5, 6, 7, 8, 4]
</code></pre>

Example 2:

Input:

<pre tabindex="0" class="chroma"><code>graph = [[0, 5, 0, 9, 1],
 [5, 0, 3, 0, 2],
 [0, 3, 0, 0, 0],
 [9, 0, 0, 0, 0],
 [1, 2, 0, 0, 0]]
start = 0
end = 2
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>shortest_path(graph, start, end) -&gt; [0, 4, 1, 2]
</code></pre>

The task is to implement a shortest path algorithm (like Dijkstra's or Bellman-Ford) to find the shortest path from a start node to an end node in a given graph. The graph is represented as a 2D array where each cell represents a node and the value in the cell represents the cost to traverse to that node.

Shortest Path Algorithms

How would you decide whether or not to create a product, like a job board, for Facebook?

Imagine Facebook is creating a job board. How would you design an A/B test to evaluate its effectiveness?

Assessing the market potential and then use A/B testing to measure its effectiveness against user behavior

Facebook Job Board Design

Let’s say you work as a data scientist at a bank.

You are tasked with building a decision tree model to predict if a borrower will pay back a personal loan they are taking out.

<ol>
<li>How would you evaluate whether using a decision tree algorithm is the correct model for the problem?</li>

<li>Let’s say you move forward with the decision tree model. How would you evaluate the performance of the model before deployment and after?</li>
</ol>

Calculate Moving Average	SQL	Easy
Predict Customer Churn	Machine Learning	Medium
A/B Test Significance	Statistics	Medium
Optimize Query Performance	SQL	Hard
Feature Importance Analysis	Machine Learning	Medium
Clean Missing Data	Python	Easy
Neural Network Architecture	Deep Learning	Hard
Calculate Cohort Retention	SQL	Medium
Bayesian Probability	Statistics	Easy
Recommend Similar Products	Machine Learning	Hard

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