Palindrome Check That Ignores Spaces, Symbols and Letter Case
Company: Walmart Labs
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Onsite
Given a string, decide whether it reads the same forwards and backwards once spaces and symbols are ignored.
The report says only that spaces and symbols must be ignored; this version also ignores letter case, as stated in Rules below.
### Function Signature
```python
def is_clean_palindrome(s: str) -> bool:
```
### Rules
- Only ASCII letters (`a` to `z`, `A` to `Z`) and digits (`0` to `9`) are compared. Every other character, including spaces and punctuation, is skipped.
- Letters are compared without regard to case: `A` equals `a`.
- Return `True` if the sequence of compared characters equals its own reverse, otherwise `False`. A string with no letters or digits counts as a palindrome and returns `True`.
### Constraints
- `0 <= len(s) <= 2 * 10^5`
- `s` contains only printable ASCII characters (codes 32 through 126).
### Examples
**Example 1**
```text
Input: s = "Was it a car or a cat I saw?"
Output: True
```
The compared characters are `wasitacaroracatisaw`, which reads the same in both directions.
**Example 2**
```text
Input: s = "12 ab 21"
Output: False
```
The compared characters are `12ab21`; the third and fourth characters, `a` and `b`, differ.
**Example 3**
```text
Input: s = "#! "
Output: True
```
No letters or digits remain.
Overview: Decide whether a string is a palindrome when spaces, punctuation and letter case are ignored and only letters and digits are compared. It tests string scanning with character filtering, case normalization and edge cases such as strings that contain no letters or digits at all.
Read the full Walmart Labs Software Engineer interview experience this question came from
Given a string `s`, decide whether it reads the same forwards and backwards once spaces and symbols are ignored. Implement `is_clean_palindrome(s)`.
**Rules**
- Only ASCII letters (`a` to `z`, `A` to `Z`) and digits (`0` to `9`) are compared. Every other character, including spaces and punctuation, is skipped.
- Letters are compared without regard to case: `A` equals `a`.
- Return `True` if the sequence of compared characters equals its own reverse, otherwise `False`. A string with no letters or digits counts as a palindrome and returns `True`.
The result is a single boolean (`true` / `false` in JavaScript, Java and C++). No value in this problem can exceed 2^31 - 1.
**Constraints**
- `0 <= len(s) <= 2 * 10^5`
- `s` contains only printable ASCII characters (codes 32 through 126).
**Example 1**
```
Input: s = "Was it a car or a cat I saw?"
Output: True
```
The compared characters are `wasitacaroracatisaw`, which reads the same in both directions.
**Example 2**
```
Input: s = "12 ab 21"
Output: False
```
The compared characters are `12ab21`; the third and fourth characters, `a` and `b`, differ.
Constraints
- 0 <= len(s) <= 2 * 10^5
- s contains only printable ASCII characters (codes 32 through 126).
Examples
Input: ('',)
Expected Output: True
Explanation: Empty string (length 0): nothing is compared, so it counts as a palindrome.
Input: ('a',)
Expected Output: True
Explanation: A single letter is a palindrome.
Hints
- Settle first which characters take part in the comparison: only a-z, A-Z and 0-9. Everything else, including characters such as '_', '@' or '[', is ignored.
- An uppercase letter and its lowercase form count as the same character. Digits have no case, so '0' never equals 'P'.
- If nothing is left once the ignored characters are removed, the answer is True.