Reverse a Character Array In Place
Company: Cargurus
Role: Data Scientist
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
The interview report preserved only the core exercise: reverse a string without using a built-in reversal method, then discuss time and space complexity. The interface and limits below are a practice-ready reconstruction of that exercise, not reported company-specific constraints.
Implement:
```python
def reverse_chars(chars: list[str]) -> None:
...
```
Reverse `chars` in place. Do not use `reversed`, slicing such as `chars[::-1]`, `list.reverse`, or another container proportional to the input size. The function must return `None`.
Constraints:
- `0 <= len(chars) <= 100_000`
- Every element is a single Unicode code point represented as a Python string.
- Use `O(n)` time and `O(1)` auxiliary space.
Examples:
```text
Input: chars = ["h", "e", "l", "l", "o"]
After: chars = ["o", "l", "l", "e", "h"]
Return: None
```
```text
Input: chars = []
After: chars = []
Return: None
```
Quick Answer: Practice an in-place character-array reversal under explicit restrictions on built-in helpers and extra storage. This coding exercise tests careful index management, mutation contracts, boundary cases, and clear time and space complexity analysis.