As the year comes to a close, the chilly wind outside carries the joy of the upcoming New Year. Yet, here we are, working hard toward our dreams. Before the clock strikes midnight, let me share a classic Google interview question—a challenge to prepare ourselves for the opportunities and hurdles of the coming year.
Problem Description: Given a string, return a new string of equal length with the same characters rearranged in decreasing order of number of occurrences. In the case of two or more distinct characters occurring the same number of times, order them by increasing character code.
Hint: Example: Given "This is a sample string", Return "sssiiiiaaTegghlmnpqrt"
Background This question is designed to test a candidate's understanding of fundamental algorithms while minimizing reliance on complex runtime libraries. Commonly featured in Google interviews, it emphasizes logical reasoning and coding skills. At first glance, it may seem straightforward, but it challenges candidates’ grasp of programming basics and language-specific features.
The interviewer began by explaining the question in detail and asked if the candidate had any questions.
Interviewer: Do you have any questions about the problem?
With real-time assistance from CSOAHelp, the candidate clearly reiterated the key aspects of the question: Candidate: The task is to arrange characters in decreasing order of frequency. If frequencies are the same, sort them by ASCII code in ascending order.
The interviewer acknowledged this restatement and moved on to discussing the solution.
CSOAHelp's Suggested Approach
CSOAHelp provided the following step-by-step guidance in real time:
- Frequency Count
- Traverse the string and use a dictionary to record the frequency of each character. If a character is already in the dictionary, increment its count; otherwise, initialize it to 1.
- Sorting
- Convert the dictionary’s key-value pairs into a list and sort it by frequency in descending order.
- For characters with the same frequency, sort them in ascending ASCII order.
- String Construction
- Based on the sorted result, repeat each character according to its frequency and append it to the new string.
The candidate, following CSOAHelp's guidance, articulated the thought process clearly: Candidate: We can first count frequencies, then sort by frequency and ASCII value, and finally construct the output string. This approach ensures the result meets all requirements.
Interviewer’s Follow-Up Questions
Interviewer: What is the time complexity of this method?
CSOAHelp prompted the candidate with the following breakdown:
- Frequency counting requires a full traversal of the string, resulting in O(n).
- Sorting takes O(k log k), where k is the number of unique characters.
- Constructing the string takes O(n). Thus, the total complexity is O(n + k log k).
The candidate repeated this explanation and elaborated further: Candidate: Since frequency counting and string construction scale with n, while sorting depends on the number of unique characters, the algorithm performs efficiently when the character set is small.
The interviewer appreciated this answer and asked another question: How would you optimize memory usage for large inputs?
CSOAHelp suggested using a streaming approach to generate the result string on demand, avoiding loading all characters at once.
The candidate restated: Using a generator to create the string incrementally can reduce memory usage, especially when handling large-scale data.
Additional Discussion and Applications
Interviewer: In real-world scenarios, where else might this character frequency problem be applied?
CSOAHelp suggested several examples:
- Text Analysis: Calculating word or letter frequencies to study language patterns.
- Data Compression: Designing efficient encoding schemes like Huffman coding based on character frequency.
- Network Traffic Analysis: Identifying frequent IP addresses in logs to detect anomalies.
The candidate summarized: This approach can be applied to text analysis, such as optimizing search algorithms by analyzing common terms; data compression by generating efficient encoding schemes; and network security to identify suspiciously frequent IP access patterns.
The interviewer appreciated these applications and provided additional real-world cases to deepen the candidate's understanding.
Candidate’s Performance
Throughout the interview, the candidate strictly followed CSOAHelp's prompts, ensuring logical and accurate responses. Particularly during follow-up questions, the candidate demonstrated a clear understanding of the problem and structured thinking, impressing the interviewer with precise communication and effective problem-solving.
Conclusion and New Year Wishes
This classic Google interview question not only tested the candidate's coding ability but also evaluated their logical reasoning and problem-solving skills. With CSOAHelp’s guidance, the candidate delivered an outstanding performance. Through this example, we hope readers can gain a better understanding of solving algorithmic challenges.
As the New Year approaches, may everyone bravely face challenges and achieve their career goals in the year ahead! Happy New Year, and may your future shine bright!
In the days to come, no matter what lies ahead, may we all write the most exciting chapters of our lives through our efforts and perseverance!
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.
