I knew there was a clever trick here but blanked on it mid-interview and just went with the brute force: try every possible prefix length that divides the total length, check if tiling it reproduces the string.
Clarify the problem and edge cases, then present an efficient solution such as checking if the string is a substring of itself doubled (excluding the first and last characters). Discuss time/space complexity and consider alternative approaches like KMP or string concatenation.
Pro tip: Mention that the doubled-string trick works because if the string is periodic, it will appear in the middle of its double; this shows deep understanding and avoids unnecessary complexity.
Ask about input constraints (e.g., string length, character set) and confirm edge cases like empty string or length 1. This demonstrates thoroughness.
Consider brute-force (checking all possible substring lengths) and optimized methods (string doubling, KMP). Explain trade-offs.
Describe the doubled-string approach: if s is a repetition, it will be a substring of (s+s) excluding the first and last characters. Provide code or pseudocode.
State time and space complexity: O(n) time with O(n) space for the doubled string, or O(1) space if using KMP on the original string.
Walk through examples like 'abab' (true) and 'aba' (false) to validate the solution and edge cases.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.