Start the New Year Strong! Arrowstreet Interview Question Breakdown: List Comprehensions Made Easy - Arrowstreet - VO support

As the New Year begins, many are setting their sights on achieving their dream jobs. For those in tech, coding interviews remain a crucial step in the hiring process. Today, we’re taking a deep dive into a real interview question from Arrowstreet, highlighting how to approach it effectively and showcasing how csoahelp provides real-time guidance to candidates throughout the process. Let’s gear up for success in 2025!

The Interview Question

Here’s the original problem statement from the interview:

Assume you have a list of names, each entry has a first and last name. Write a list comprehension to generate the permutations of names, excluding the last names that are longer than 7 characters.

For example, given the input:

names = ["John Smith", "Sally Anderson", "Ashwin Long", "Mandy Kim"]

Expected output:

['John Smith', 'John Long', 'John Kim',
 'Sally Smith', 'Sally Long', 'Sally Kim',
 'Ashwin Smith', 'Ashwin Long',
 'Mandy Smith', 'Mandy Long', 'Mandy Kim']

Requirement:
Your answer should be a single line of code. Assume that there is an existing variable names containing a list of input names.

Understanding the Problem

The interview starts with the interviewer explaining the problem, and the candidate seeking clarifications to ensure they fully understand the task.

Interviewer:
The task involves generating all permutations of names using the first names and last names provided, but you’ll need to exclude any last names that are longer than 7 characters. Additionally, you should implement this in a single line of code using a Python list comprehension.

csoahelp (real-time guidance):
You can ask clarifying questions such as:

What should the function return if the input list is empty?
Should duplicates in the input list be handled or ignored?
Are first and last names guaranteed to be separated by a single space?

Candidate:
Thank you for the problem description. I’d like to confirm a few details:

If the input list is empty, should the result also be an empty list?
Are duplicates in the input list expected to persist in the output?
Can I assume that each name is properly formatted with a single space separating the first and last names?

Interviewer:
Great questions! If the input list is empty, the output should also be an empty list. Duplicates in the input can remain as they are—no need to handle them. And yes, you can assume the names are well-formatted with a single space separating the first and last names.

Developing the Solution

With the problem fully understood, the candidate begins explaining their thought process. Here, csoahelp steps in to ensure their reasoning is clear and comprehensive.

Candidate:
To solve this problem, I’d break it into three steps:

First, split each name into its first and last names.
Then, filter out any last names longer than 7 characters.
Finally, use a nested list comprehension to combine all valid first names with valid last names to create permutations.

csoahelp (real-time guidance):
Here’s how you can refine your explanation:

Mention explicitly that you’ll use Python’s split() method to separate names into first and last names.
Highlight that filtering is done using a conditional check inside the comprehension.
Explain that the nested structure of the list comprehension allows for pairing every first name with every valid last name.

Candidate:
Specifically, I’ll use Python’s split() method to separate each name into its first and last components. Then, I’ll apply a condition to filter out last names whose length exceeds 7 characters. Using a nested list comprehension, I’ll iterate over all first names and pair them with the filtered last names to create all possible combinations.

Interviewer:
That sounds good. How would you implement it as a single line of code?

Writing the Code

The interviewer then challenges the candidate to present their solution concisely. With csoahelp’s guidance, the candidate confidently describes the final implementation.

csoahelp (real-time guidance):
You can describe the nested list comprehension step-by-step while keeping the code concise. For example:

Outer loop iterates over first names.
Inner loop filters and iterates over last names that meet the condition.
Combine the first name and last name with a space in between.

Candidate:
Here’s how I’d write it as a single line of code:

result = [f"{fn} {ln}" for fn, ln in ((name.split()[0], name.split()[1]) for name in names) if len(ln) <= 7]

This list comprehension:

Splits each name into fn (first name) and ln (last name).
Filters out last names longer than 7 characters using the condition if len(ln) <= 7.
Combines valid first and last names into a single string using f"{fn} {ln}".

Complexity Analysis

The interviewer asks the candidate to analyze the solution’s complexity, and csoahelp assists with framing a concise yet accurate answer.

Interviewer:
Can you explain the time complexity of your solution?

csoahelp (real-time guidance):
Break the analysis into two parts:

Splitting names into first and last components—linear in the number of names.
Nested iteration to create permutations—quadratic if all last names are valid.

Candidate:
Sure. The time complexity can be analyzed as follows:

Splitting each name into first and last names is O(n), where n is the length of the input list.
Generating permutations involves iterating over all first names and valid last names. If most last names are valid, this step is approximately O(n²).

So the overall complexity is approximately O(n²).

Behavioral Questions and Closing

After completing the technical portion, the interview transitions to behavioral questions.

Interviewer:
Can you share an example of a time you solved a challenging problem in a collaborative setting?

csoahelp (real-time guidance):
Highlight a project where you faced a significant challenge. Structure your response around:

The problem.
Your role in solving it.
The outcome.

Candidate:
During my internship, I worked on a data pipeline project that faced significant delays in processing due to poorly optimized SQL queries. I collaborated with my team to analyze query performance, identified bottlenecks, and redesigned the queries to reduce runtime by 50%. My role involved both identifying the problem and implementing the new solution. This taught me the importance of systematic debugging and teamwork.

Interviewer:
Great example! Thanks for sharing. Good luck, and have a happy New Year!

The Value of csoahelp: Your Real-Time Interview Assistant

Throughout this interview, csoahelp provided key advantages to the candidate:

Understanding the Problem: Guiding the candidate to ask clarifying questions to ensure a solid grasp of the requirements.
Explaining the Solution: Offering a clear framework to articulate their thought process and approach.
Handling Complexity Analysis: Helping the candidate break down time complexity in a structured way.
Answering Behavioral Questions: Assisting the candidate in crafting impactful stories that demonstrate problem-solving and collaboration skills.

With csoahelp, candidates can approach every interview with confidence and clarity, turning even the most challenging questions into an opportunity to shine.

New Year, New Opportunities

As you set your career goals for the New Year, let csoahelp be your trusted partner in achieving them. With real-time guidance, personalized advice, and expert insights, you can tackle every interview with confidence and make 2025 your year of success. Happy New Year, and good luck on your job search!

经过csoahelp的面试辅助，候选人获取了良好的面试表现。如果您需要面试辅助或面试代面服务，帮助您进入梦想中的大厂，请随时联系我。

If you need more interview support or interview proxy practice, feel free to contact us. We offer comprehensive interview support services to help you successfully land a job at your dream company.