Palindrome Check

What they ask

A warm-up in the coding round: given a string, return whether it reads the same forwards and backwards. The interviewer then tightens it: ignore case, ignore non-alphanumeric characters, and do it without building a reversed copy.

Because this round is about how you work rather than the puzzle, they expect you to write a test first (they care about TDD), then the implementation, then refactor.

Examples

• "level" returns true.
• "Talabat" returns false.
• "A man, a plan, a canal: Panama" returns true once punctuation and case are ignored.
• "" returns true.

Constraints

• Up to 10^5 characters.
• O(n) time, O(1) extra space for the two-pointer version.

What they look for

• Starting from tests, small commits, readable names.
• Two pointers moving inward, skipping non-alphanumerics, comparing lowercase.
• Asking clarifying questions (Unicode? whitespace?) before coding.
• Talking through the second problem they add in the same session, typically sum of the two smallest numbers or moving zeros in an array.