Stripe's technical interviews are known for their focus on real-world scenarios and logical problem-solving. This interview task revolves around logistics pathfinding and shipping cost calculation, covering both direct and single-transfer paths. In this blog, we will provide a detailed reconstruction of the interview scenario, including how CSOAHelp provided real-time assistance to help the candidate tackle each part of the problem step-by-step.
Interview Question Background
The logistics problem is designed to simulate real-world scenarios where Stripe manages shipping routes across multiple countries. The task is divided into two parts:
- Direct Path Cost Calculation: Calculate the shipping cost for a direct route between two countries.
- Single-Transfer Path Calculation: If no direct route exists, support the calculation for a path involving one intermediate country.
Part 1: Direct Path Cost Calculation
Problem Description
The candidate was tasked to write a function that takes the following parameters:
- Source country.
- Target country.
- Shipping method.
The function must return the shipping cost using the provided input data. For example:
inputString = "US:UK:FedEx:5,UK:FR:DHL:2,US:CA:FedEx:7,CA:US:UPS:4"
If the input is "US", "UK", "FedEx", the function should return:
5
Clarification and Initial Discussion
Candidate's Key Questions:
- Candidate: Are there duplicate routes in the input data?
Interviewer: No, you can assume each route is unique. - Candidate: Can I assume the input format is always valid?
Interviewer: Yes, the format will always be correct, but the requested path may not exist. - Candidate: Should direct paths always take priority?
Interviewer: Yes, if a direct path exists, it should always be used.
Algorithm Design
Candidate: I plan to parse the input data and store it in a structured format, such as a hash map, to facilitate fast lookups.
Interviewer: That sounds reasonable. How would you structure the data?
CSOAHelp Suggestion: Use a hash map where:
- The key is the source country.
- The value is a list of arrays containing the destination country, shipping method, and cost.
For example:
"US" -> [["UK", "FedEx", "5"], ["CA", "FedEx", "7"]]
Candidate: This structure allows me to:
- Parse the input string into individual routes.
- Store each route's details in the map.
- Use the source country to quickly access possible routes and filter based on the target country and method.
Mock Interview Dialogue
Candidate: If the input specifies "US", "UK", "FedEx", I will first retrieve all routes originating from the US. Then, I'll match the target country and method to find the correct cost.
Interviewer: That approach makes sense. What will you return if no route matches?
CSOAHelp Suggestion: Return null or an error message to handle such cases gracefully.
Summary of Part 1
This part focused on building an efficient data structure to solve the problem in constant or near-constant time for direct routes. CSOAHelp guided the candidate through the critical decisions, ensuring the implementation was robust and scalable.
Part 2: Single-Transfer Path Calculation
Problem Description
When no direct route exists, the candidate was tasked to calculate the cost of a path involving one intermediate country. For example:
inputString = "US:UK:FedEx:5,UK:FR:DHL:2,US:CA:FedEx:7,CA:US:UPS:4"
If the input is "US", "FR", the result should be:
route: "US -> UK -> FR"
method: "FedEx -> DHL"
cost: 7
Clarification and Detailed Discussion
Candidate's Key Questions:
- Candidate: Can the path include more than one intermediate country?
Interviewer: No, only one intermediate country is allowed. - Candidate: What if both direct and single-transfer paths are available?
Interviewer: The direct path should take precedence. - Candidate: Should the function return an error if no valid path exists?
Interviewer: Yes, it should indicate that no path was found.
Algorithm Design
Candidate: I will modify the earlier hash map structure to account for intermediate routes. Here's my approach:
- Search for a direct route first.
- If no direct route exists, iterate over all possible intermediate countries.
- For each intermediate country:
- Check if a route exists from the source to the intermediate country.
- Check if a route exists from the intermediate country to the target country.
- Combine the results to form the full path and calculate the total cost.
Interviewer: How would you ensure the intermediate search is efficient?
CSOAHelp Suggestion: Split the solution into two phases:
- Phase 1: Query the hash map for direct paths.
- Phase 2: For intermediate paths, iterate through the map keys and calculate the cost dynamically.
Mock Interview Dialogue
Candidate: For a query like "US", "FR", I would first check if there's a direct route. If not, I would try "US -> UK -> FR" and "US -> CA -> FR".
Interviewer: What if there are multiple intermediate paths?
CSOAHelp Suggestion: Prioritize the path with the lowest cost or return the first valid path.
Candidate: Are there edge cases I should consider, such as missing countries?
CSOAHelp Suggestion: Handle invalid inputs gracefully by returning a clear error message.
Final Reflections
The Stripe interview questions tested the candidate's ability to design scalable solutions for real-world scenarios. By providing critical guidance, CSOAHelp ensured that:
- The candidate clarified all ambiguities upfront.
- The solution was optimized for performance and scalability.
- Edge cases were handled comprehensively.
Stripe's emphasis on problem-solving, combined with CSOAHelp's detailed support, allowed the candidate to deliver a robust and well-thought-out solution. If you're preparing for a similar interview, CSOAHelp is here to assist you every step of the way!
如果您也想在面试中脱颖而出，欢迎联系我们。CSOAHelp 提供全面的面试辅导与代面服务，帮助您成功拿到梦寐以求的 Offer！
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.
