How would you sort filenames with numeric segments?
Company: Hopper
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
You are given a list of filename strings (e.g., `"file10.txt"`, `"file2.txt"`, `"10file.txt"`). Implement a custom sort for these strings using a comparator with the following rules:
1. **Digit-first at the first differing position**: When comparing two strings from left to right, if at the first position where they differ one string has a digit (`0-9`) and the other has a non-digit, the digit one should come first.
2. **Numeric comparison for digit runs**: Treat any **maximal consecutive digit substring** as a single number and compare by **numeric value** (so `"file10.txt"` comes after `"file2.txt"`).
3. **Normal character order for non-digit runs**: Compare non-digit parts in standard character/lexicographic order.
Return the filenames sorted according to these rules.
Follow-ups:
- **Leading zeros**: How should `"file01.txt"` and `"file1.txt"` be ordered if their numeric values are equal? Implement your chosen tie-break rule.
- **Performance**: If there are very many filenames, repeatedly parsing digit runs inside the comparator can be slow. How would you optimize the sorting implementation?
Quick Answer: This question evaluates a candidate's ability to design custom string comparators, parse maximal digit runs and compare numeric values, and handle edge cases such as leading zeros and digit-versus-non-digit ordering.
Sort filenames using digit-first comparison, numeric comparison for digit runs, and lexicographic comparison for non-digit runs. Equal numeric values tie by shorter digit run then raw digits.
Constraints
- Inputs are Python literals matching the function signature.
- Return a deterministic exact-match value.
Examples
Input: (['file10.txt','file2.txt','10file.txt'],)
Expected Output: ['10file.txt', 'file2.txt', 'file10.txt']
Explanation: Numeric runs and digit-first.
Input: (['file01.txt','file1.txt','file001.txt'],)
Expected Output: ['file1.txt', 'file01.txt', 'file001.txt']
Explanation: Leading-zero tie-break.
Hints
- Model object-style prompts as operation streams when needed.
- Handle empty and boundary cases before the main logic.