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Enersys Interview Questions

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Data Structures & Algorithms

Given an integer N, write a function that returns all of the prime numbers up to N

Prime to N

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

Write a function that tests whether a string of brackets is balanced.

The Brackets Problem

Implement a fixed-length array with addition, deletion, and search operations.

Fixed-Length Arrays: Deletion

Behavioral

Describing a data project and its challenges

Hurdles In Data Projects

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

Why Do You Want to Work With Us

How would you negotiate and resolve disagreements when a client rejects your proposed solution?

Client Solution Pushback

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

Your Strengths and Weaknesses

Machine Learning

How would you investigate the cause of this training instability?

Training Instability in Neural Networks

Let's say that you're training a classification model.   How would you combat overfitting when building tree-based models?

Overfit Avoidance

Create top_ads with the top 3 ads and return the row counts for inner, left, right, and cross joins with ads

Size of Joins

Supply Chain

How would you decide on a metric and approach for worker allocation across an uneven production line?

Worker Distribution Dilemma

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

Given an integer <code>N</code>, write a function that returns a list of all of the prime numbers up to <code>N</code>.

Note: Return an empty list there are no prime numbers less than or equal to <code>N</code>.

Example:

Input:

<pre tabindex="0" class="chroma"><code>N = 3
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def prime_numbers(N) -&gt; [2,3]
</code></pre>

You’re given a string that may contain the characters <code>{</code>, <code>}</code>, <code>[</code>, <code>]</code>, <code>(</code>, and <code>)</code>.

Task: Verify that the string is balanced. A balanced string is one where every opening character, <code>{</code>, <code>[</code>, or <code>(</code>, has a corresponding closing character, <code>}</code>, <code>]</code>, or <code>)</code>.

Write a function called <code>is_balanced(string: str) -&gt; bool</code> which verifies the balance of a string.

Example:

<pre tabindex="0" class="chroma"><code>is_balanced(&#39;(())[]{}&#39;) -&gt; True
</code></pre>

<pre tabindex="0" class="chroma"><code>is_balanced(&#39;{([(){}])()}&#39;) -&gt; True
</code></pre>

<pre tabindex="0" class="chroma"><code>is_balanced(&#39;{}[]())&#39;) -&gt; False
</code></pre>

<hr/>

Let’s say you work at Allstate. Allstate is running <code>N</code> online ads right now. The table <code>ads</code> contains all those ads, ranked by popularity via the <code>id</code> column (e.g., the entry with <code>id = 1</code> is the most popular, etc.).

Create a subquery or common table expression named <code>top_ads</code> containing the top 3 ads (by popularity) and return the number of rows that would result from the following operations

<ol>
<li><code>ads INNER JOIN top_ads</code></li>
<li><code>ads LEFT JOIN top_ads</code></li>
<li><code>ads RIGHT JOIN top_ads</code></li>
<li><code>ads CROSS JOIN top_ads</code></li>
</ol>

Note: Please make the <code>join_type</code> column in your output have the values <code>inner_join</code>, <code>left_join</code>, etc. for each of their respective join types

Note: Please return only one query with each number in a different row

Example:

Input:

<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>
Output:

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

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

<tr>
<td><code>number_of_rows</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>

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.

Tell me about a data project that didn’t go the way you expected. What did you set out to do, what surprised you, and how did you handle it?

You’re AI engineer working on an energy forecasting system at Siemens that helps utilities predict short-term electricity demand to balance grid load and reduce outages. You train a recurrent neural network on long historical time series (weather, calendar effects, local demand signals) to forecast energy demand.

Early in training, the model appears to learn normally, but after several epochs the loss becomes highly unstable, oscillating wildly before turning into NaNs. At the same time, training slows dramatically and the model fails to recover even after restarting from recent checkpoints.

You’ve verified that the data pipeline is correct and labels are well-aligned with inputs. No changes were made to the dataset, but increasing the sequence length or learning rate makes the problem significantly worse.

How would you investigate the cause of this training instability? What signals would you look for during debugging, and how would those findings guide the changes you make to the model or training setup?

Let’s say you work as a data architect at Facebook.

Facebook is trying to transition their product from just doing likes on posts and comments to adding the multi-reaction under the like button.

How would you approach this problem? What would the database modifications look like?

How would you approach adding multi-reactions under the like button and what database modifications would you make

Multi-Reaction

Data Modeling

Let’s say that you’re training a classification model.

How would you combat overfitting when building tree-based models?

Let’s say we’re managing a production line for assembling electric scooters, with 10 stations where each has a different average processing time per unit (for example, Station 1 takes 5 minutes, Station 2 takes 3 minutes, and so on).

How would you determine the right metric to use for balancing worker allocation across the stations, and how would you use it to figure out how many workers each station needs?

Let’s say we have a search form in our web app where users can enter a keyword like “star”, and the system searches for matches across several different fields in a large database table. Lately, these searches have been timing out when users search for common words.

How would you approach diagnosing and resolving these search timeouts?

How would you resolve slow, timing-out keyword searches across multiple database fields?

Search Timeout

Product Sense & Metrics

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

You are a pirate who has discovered a chest full of gold coins. Each coin has a value, represented as an integer in the array <code>coins</code>.

Your mission is to find the kᵗʰ most valuable coin — the one that ranks <code>k</code> from the top in value.

Note: We are looking for the kᵗʰ largest coin by value, not necessarily a unique value.

Can you find it without sorting all the coins?

<h3>Example 1</h3>

Input:

<pre tabindex="0" class="chroma"><code>coins = [3, 2, 1, 5, 6, 4], k = 2
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def find_kth_treasure(coins, k) -&gt; 5
</code></pre>

Explanation:

<pre><code>The sorted treasure values are [6, 5, 4, 3, 2, 1]. The 2nd largest coin has value 5.
</code></pre>

<h3>Example 2</h3>

Input:

<pre tabindex="0" class="chroma"><code>coins = [3, 2, 3, 1, 2, 4, 5, 5, 6], k = 4
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def find_kth_treasure(coins, k) -&gt; 4
</code></pre>

Explanation:

<pre><code>Sorted values are [6, 5, 5, 4, 3, 3, 2, 2, 1]. The 4th largest coin is 4.
</code></pre>

<h3>Constraints</h3>

<ul>
<li><code>1 &lt;= k &lt;= coins.length &lt;= 10^5</code></li>
<li><code>-10^4 &lt;= coins[i] &lt;= 10^4</code></li>
</ul>

The Pirate’s Hunt

Probability

You have been tasked with designing three classes: <code>text_editor</code>, <code>moving_text_editor</code>, and <code>smart_text_editor</code>. These classes are to be created with specific functionalities as defined below:

<ol>
<li><code>text_editor</code> class:

<ul>
<li><code>write_line(string:str)</code>: A method which appends a given string to the end of the existing string.</li>
<li><code>delete_line(char_num : int)</code>: A method which deletes <code>char_num</code> number of characters from the existing string, starting from the end. If there are no characters left, the method should do nothing.</li>
<li><code>special_operation()</code>: A method which currently does nothing.</li>
<li><code>get_notes()</code>: A method which returns the internal string.</li>
</ul></li>

<li><code>moving_text_editor</code> class:

<ul>
<li>This class extends <code>text_editor</code>. The <code>special_operation()</code> method is overridden. Initially, the cursor will be at the end of the current string. If <code>special_operation()</code> is called, it moves the cursor to the beginning of the string, any additional appends will be appended to the beginning of the string instead. Calling <code>special_operation()</code> again reverses the cursor operation.</li>
</ul></li>

<li><code>smart_text_editor</code> class:

<ul>
<li>This class extends <code>text_editor</code>. In this class, the <code>special_operation()</code> method is overridden to serve as an undo operation, allowing it to undo an infinite number of operations.</li>
</ul></li>
</ol>

<h3>Input</h3>

<pre tabindex="0" class="chroma"><code>[[&#39;special_text_editor&#39;], [&#39;write_line&#39;, &#39;special_operation&#39;, &#39;write_line&#39;], [&#39;World&#39;, &#39;Hello, &#39;]]
</code></pre>

<h3>Output</h3>

<code>&#34;Hello, World&#34;</code>

Create a text editor while displaying method overriding as a concept.

Text Editor With OOP

Design Patterns

How many gas stations are there in the United States?

How would you estimate the number of gas stations in the US without direct data?

Gas Station Counting

Estimation

You were asked to forecast sales for a retail chain with strong seasonal patterns using seasonal ARIMA (SARIMA).

How would you justify using SARIMA in this context, and how does it compare to other time series forecasting techniques?

Compare SARIMA to other time series models for seasonal sales forecasting.

SARIMA in Retail Forecasting

Forecasting & Time Series

Important: You must answer <a href="https://www.interviewquery.com/questions/array-operations-fixed-length-arrays-1">this question</a> before attempting this one. We recommend copying your previous solution and iterating the new solution with the added operations.

Create a more extensive <code>Array</code> class simulating the functionality of fixed-size arrays. The array’s fixed size is <code>6</code>. In this question, we will be implementing the deletion and search operations.

<ul>
<li><code>pop_back() -&gt; element</code> - removes the last element of the array. Returns the removed element. If the array is empty, return <code>None</code>.</li>

<li><code>pop_front() -&gt; element</code> - removes the first element of the array. Returns the removed element. If the array is empty, return <code>None</code>.</li>

<li><code>pop(index) -&gt; element</code> - removes the element at the specified index and returns it. When the index is not in range, raise an <code>IndexError</code>.</li>

<li><code>search(element) -&gt; index</code> - searches for the specified element and returns the index of the first instance if it exists inside the array. Returns <code>-1</code> if the element does not exist inside the array. Example: <code>Array([1, 2, 3]).search(2) -&gt; 1</code>.</li>

<li><code>__contains__(element) -&gt; bool</code> - checks if the element exists inside the array. Returns <code>True</code> if it exists and <code>False</code> if it does not.</li>

<li><code>abolish(element) -&gt; count</code> - removes all instances of an element and returns the count of all removed instances.</li>

<li><code>__eq__(other) -&gt; bool</code> - checks the equality of the array with another array called <code>other</code>. Raises a <code>TypeError</code> if <code>other</code> is not an instance of this custom <code>Array</code> class.</li>
</ul>

Note: All the basic addition operations must be implemented first. (Refer to Fixed Length Arrays 1)

Let’s say you’re building an interactive Tableau dashboard for Fabletics’ merchandising team to help them monitor weekly sales performance across different product categories and regions.

How would you explain the difference between filters and parameters in Tableau to a non-technical stakeholder, and in what kinds of scenarios would you recommend using each one on this dashboard?

How would you explain and apply filters versus parameters on a Fabletics sales dashboard?

Tableau Filters and Parameters

Data Viz & Interpretation

Let’s say we’re responsible for deploying a new version of Uber’s routing system, and the release includes both backend and frontend changes that may impact user workflows.

How would you design the deployment process to minimize risk, ensure clear communication with both clients and internal teams, and handle rollbacks if unexpected issues arise?

How would you structure a safe deployment process with effective stakeholder communication and rollback plans?

Safe Deployments

DevOps

Let’s say we’re launching a new version of the PayPal app, but due to a tight deadline, we don’t have time to run the entire suite of 300 automated test cases before release.

How would you handle this situation?

How would you approach limited testing time before a major app release?

Testing Constraints

A/B Testing

Let’s say we’ve proposed a new analytics dashboard to a client, but after reviewing our design and data sources, the client says the solution doesn’t meet their needs and pushes back on several key features.

How would you approach the conversation to negotiate alternative solutions, and what steps would you take to ensure disagreements are handled constructively so we can still reach a successful outcome?

Tell me about a project in which you had to clean and organize a large dataset.

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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