In this blog post, we’ll dive into one of Lyft’s challenging interview problems: the shortest word transformation sequence. We’ll break down the problem-solving process, clarify the steps involved, address potential edge cases, and highlight how csoahelp provides valuable guidance throughout every phase of the interview.
Problem: Shortest Transformation Sequence
Problem Statement (Original):
"A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:
- Every adjacent pair of words differs by a single letter.
- Every
sifor1 <= i <= kis inwordList. Note thatbeginWorddoes not need to be inwordList. sk == endWord.
Given two words, beginWord and endWord, and a dictionary wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, or 0 if no such sequence exists.
Example 1:
- Input:
beginWord = "hit",endWord = "cog",wordList = ["hot", "dot", "dog", "lot", "log", "cog"] - Output:
5 - Explanation: The shortest transformation sequence is
hit -> hot -> dot -> dog -> cog, which is 5 words long.
Example 2:
- Input:
beginWord = "hit",endWord = "cog",wordList = ["hot", "dot", "dog", "lot", "log"] - Output:
0 - Explanation: The
endWorddoes not exist in thewordList.
Step 1: Clarifying the Problem
At the beginning of the interview, clarifying the question is crucial to avoid any misunderstandings:
Candidate:
“Can I assume that all words in the input, including beginWord and endWord, have the same length? And is the input guaranteed to be non-empty?”
Interviewer:
“Yes, all words are guaranteed to be of the same length, and beginWord and endWord are valid, non-empty strings.”
csoahelp Insight:
Clarifying the problem’s constraints builds confidence and demonstrates attention to detail. csoahelp extensively trains candidates to master this step.
Step 2: Developing the Approach
After clarifying the problem, the candidate begins formulating the solution:
Candidate:
“This problem can be treated as a graph shortest path problem, where each word is a node. Two words are connected if they differ by only one letter. I plan to use Breadth-First Search (BFS) because it’s ideal for finding the shortest path in an unweighted graph.”
Interviewer:
“Interesting approach. How will you generate neighboring words for a given word?”
Candidate:
“I’ll modify each character of the word one at a time, replacing it with every possible letter (‘a’ to ‘z’), and check if the resulting word exists in the wordList. If it does, I’ll add it to the next level of the BFS queue.”
csoahelp Contribution:
During preparation sessions, csoahelp emphasizes the importance of articulating solutions clearly. Candidates learn to describe graph-related problems and BFS effectively.
Step 3: Addressing Edge Cases
The interviewer then probes deeper, asking about potential edge cases:
Interviewer:
“What happens if the endWord is not present in the wordList? Or if wordList is extremely large?”
Candidate:
“If the endWord is not in the wordList, I’ll return 0 immediately since no transformation is possible.
For a large wordList, I can optimize my BFS using bidirectional BFS. By searching simultaneously from beginWord and endWord, I can significantly reduce the search space.”
Interviewer:
“Good. Can you explain why bidirectional BFS improves efficiency?”
Candidate:
“Bidirectional BFS works by reducing the depth of the search from both ends. Instead of traversing the graph fully in one direction, the search stops when the two BFS levels meet in the middle, cutting down the total search time.”
csoahelp Key Tip:
csoahelp teaches candidates how to anticipate edge cases and optimize solutions under time constraints, ensuring they stand out in challenging interviews.
Step 4: Complexity Analysis
After presenting the solution, the candidate summarizes the time and space complexity:
Candidate:
“The time complexity for single-source BFS is O(N * M^2), where N is the size of the wordList and M is the length of each word.
With bidirectional BFS, the search depth is reduced, which further optimizes the time complexity.
The space complexity is O(N) for storing the visited words and the queue.”
Interviewer:
“That’s a thorough explanation. Great work.”
csoahelp Advantage:
In preparation, candidates practice summarizing time and space complexities, ensuring they deliver concise and accurate conclusions.
Step 5: Behavioral Question
As the technical round concludes, the interviewer transitions to a behavioral question:
Interviewer:
“Can you describe a situation where you solved a complex problem under tight deadlines?”
Candidate:
“During my previous internship, I encountered a system bug just hours before a major product demo. I quickly analyzed the logs, identified the root cause, and implemented a temporary fix. I also coordinated with my team to ensure that a permanent solution was developed afterward. This experience taught me how to stay calm under pressure and focus on critical tasks.”
csoahelp Support:
Through targeted mock interviews, csoahelp helps candidates craft polished, impactful responses to behavioral questions that highlight problem-solving abilities and teamwork.
Conclusion: Why csoahelp Makes a Difference
In this Lyft interview example, the candidate successfully:
- Clarified the problem constraints.
- Presented a structured solution using BFS and bidirectional BFS.
- Handled edge cases and explained optimizations.
- Summarized time and space complexities clearly.
- Delivered an excellent behavioral response.
This polished performance was no accident. csoahelp provides:
- Systematic training on graph problems and optimization strategies.
- Realistic mock interviews that prepare candidates for technical challenges and follow-up questions.
- Behavioral interview coaching that highlights each candidate’s strengths.
If you’re preparing for technical interviews at companies like Lyft, csoahelp can guide you every step of the way to ensure you walk into your interview with confidence—and walk out with an offer!
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.
