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Umicore Interview Questions

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Machine Learning

Which model would perform better and why?

Booking Regression

Lasso vs Ridge

Find the linear regression parameters of a given matrix

Linear Regression Parameters

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

Behavioral

Describing a data project and its challenges

Hurdles In Data Projects

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

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

Statistics

What are the assumptions of linear regression?

Assumptions of Linear Regression

How do you detect and handle correlation between variables in linear regression, and what happens if you ignore it

Correlation in Regression

What are the regression coefficients when regressing Y on X versus X on Y, given Y = X plus normal white noise?

Regress Y on X

Product Sense & Metrics

The role of A/B testing in measuring the success rate of an analytics experiment

Success Measurement

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

Search Timeout

Vision Setting and Execution Strategy

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

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?

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>

Let’s say we want to build a model to predict booking prices on Airbnb.

Between linear regression and random forest regression, which model would perform better and why?

What are the two key concepts of random forest regression?

What are the two key concepts of random forest regression?

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/>

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.

What’s the difference between Lasso and Ridge Regression?

Under what circumstances is it recommended to use Lasso regression over Ridge regression?

Under what circumstances is it recommended to use Lasso regression over Ridge regression?

What are the assumptions of linear regression?

Which assumption of the residuals of the standard linear regression model can not be overcome by increasing the sample size?

Regression assumptions

You’re a data scientist at YouTube. Leadership wants to revisit how the platform measures success, not for a specific new feature, but for the product as a whole given its current state.

How would you define and measure success for YouTube? Identify your primary and secondary metrics, explain your rationale for each, and discuss how you would choose the right thresholds for any engagement-based metrics you propose.

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 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?

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

Worker Distribution Dilemma

Supply Chain

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?

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

Describing a real-world data cleaning and organization project

Data Cleaning Experiences

Analytics

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

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 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

Describe a time when you had to define a long-term vision for a project or team and move it from concept to reality.

Interviews for leadership or senior technical roles look for more than just “finishing a project.” Your answer should specifically address:

<ol>
<li>The “Why”: What data or organizational gap necessitated this vision?</li>
<li>The Framework: How did you translate a high-level goal into a roadmap?</li>
<li>The Friction: How did you handle stakeholders or team members who were skeptical of the new direction?</li>
</ol>

Talk about a time when you had trouble communicating with stakeholders. How were you able to overcome it?

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 a matrix of X and y values, write a function to generate a transposed matrix and estimate the parameters for linear regression.

Example:

Input:

<pre tabindex="0" class="chroma"><code>A = [[1, 5], [4,8], [5,9]]

</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>#Output
linear_regression(A) -&gt; [[[1, 4, 5], [5, 8, 9]] , [4, 1]]
</code></pre>

Note: Return the solutions a list of `[[A_T] , [coefficients]]

How do you detect and handle correlation between variables in linear regression? What will happen if you ignore the correlation in the regression model?

Suppose we have two variables, X and Y, where Y = X + some normal white noise.

<ol>
<li>What will our coefficient be if we run a regression of Y on X?</li>

<li>What happens if we run a regression of X on Y?</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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