Technical interviews at Bloomberg are known for testing a candidate's algorithmic skills, logical thinking, and problem-solving ability under pressure. In this blog, we will break down a question involving numbers divisible by 3 with one digit change. We'll also highlight how CSOAHelp can guide candidates through similar challenging problems and help them ace their interviews.
Problem Statement:
You are given a string
S, consisting ofNdigits, that represents a number. You can change at most one digit in the string to any other digit. How many different numbers divisible by 3 can be obtained in this way?Write a function:
class Solution { public int solution(String S); }that, given a string
Sof lengthN, returns an integer specifying how many numbers divisible by 3 can be obtained with at most one change of a digit.
Examples:
- Given
S = "23", the function should return7.
Numbers:"03","21","24","27","33","63","93". - Given
S = "0081", the function should return11.
Numbers:"0021","0051","0081","0084","0087","0381","0681","0981","3081","6081","9081". - Given
S = "022", the function should return9.
Numbers:"012","021","024","027","042","072","222","522","822".
Clarification Phase: Ensuring Understanding of Requirements
Before diving into the solution, the candidate asked clarifying questions to make sure they fully understood the problem:
Candidate:
"Am I allowed to change any digit in the string? Should I handle cases with leading zeros?"
Interviewer:
"Yes, you can change any digit. Leading zeros are acceptable; just ensure that the resulting number is divisible by 3."
CSOAHelp’s Role:
At CSOAHelp, we prepare candidates to ask targeted clarifying questions, such as confirming constraints like “at most one change” or handling leading zeros. This ensures candidates avoid misunderstandings and proceed with confidence.
Solution Discussion: Formulating the Core Approach
After clarifying the requirements, the candidate proceeded to explain their solution:
Candidate:
"My plan is to first calculate the sum of the digits in the given string. Then, for each digit in the string, I'll try replacing it with all possible digits (0-9) and check if the new sum is divisible by 3. If it is, I count that as a valid result."
Interviewer:
"Sounds good. Can you elaborate on how you calculate divisibility by 3?"
Candidate:
"To check if a number is divisible by 3, I just need to determine if the sum of its digits is divisible by 3. For each potential change, I’ll adjust the digit's contribution to the sum and check if the new sum satisfies the condition."
CSOAHelp’s Role:
We train candidates to break down complex problems into manageable steps and communicate their thought process clearly. By practicing similar problems, candidates learn to articulate both their logic and methodology effectively.
Handling Edge Cases and Follow-Up Questions
The interviewer posed additional questions to test the candidate’s depth of understanding:
Interviewer:
"What happens if the string has repeated digits? Does your solution still work efficiently?"
Candidate:
"Yes, my solution works even if there are repeated digits. For each digit, I simulate replacing it with all other values (0-9), and the computation for each digit is independent of the others."
Interviewer:
"What is the time complexity of your solution? Can you optimize it further?"
Candidate:
"The current time complexity is O(N × 10), where N is the length of the string, and 10 represents the possible replacements for each digit. This can be optimized by precomputing the sum and only recalculating the effect of each change instead of recalculating the sum for every attempt."
CSOAHelp’s Role:
We guide candidates in analyzing time complexity systematically and brainstorming potential optimizations. This preparation helps them respond confidently to follow-up questions, demonstrating both technical expertise and adaptability.
Complexity Analysis and Solution Summary
After addressing the follow-up questions, the candidate summarized their approach:
Candidate:
"The solution involves iterating through each digit in the string, trying all possible replacements (0-9), and checking if the resulting number is divisible by 3. The time complexity is O(N × 10), and the space complexity is O(1), as no additional data structures are used."
Interviewer:
"That’s a solid approach and sufficient for this problem."
CSOAHelp’s Role:
We help candidates refine their ability to succinctly summarize solutions, including time and space complexity. This ensures they leave a strong impression on the interviewer.
Behavioral Questions: Showcasing Soft Skills
After the technical discussion, the interviewer shifted to behavioral questions:
Interviewer:
"Can you describe a time when you faced a tight deadline and how you handled it?"
Candidate:
"In one of my previous projects, I was tasked with optimizing a data processing pipeline under a tight deadline. I focused on identifying the key bottlenecks and introduced parallel processing to speed up the system. By prioritizing critical tasks and collaborating effectively with my team, we delivered the solution on time and exceeded performance expectations."
CSOAHelp’s Role:
We prepare candidates for behavioral questions by using the STAR framework (Situation, Task, Action, Result). This helps them structure their answers clearly and highlight their problem-solving and teamwork skills.
Conclusion
With CSOAHelp’s comprehensive guidance, this candidate successfully navigated Bloomberg’s challenging algorithm interview. From problem understanding to solution optimization and handling behavioral questions, every step was backed by rigorous preparation and practice.
If you’re preparing for your next technical interview, CSOAHelp is here to provide personalized support and ensure you’re ready to tackle even the most complex challenges. Let us help you achieve your career goals!
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.
