Start by clarifying the requirements: case sensitivity and Unicode handling. Then propose an efficient solution using a set of characters from the reference string for O(1) lookups, and iterate through each string checking for intersection. Discuss trade-offs between preprocessing the reference string versus each string, and how to handle Unicode normalization and case folding.
Pro tip: Mention that using a set of characters from the reference string is efficient, but if the list is large and strings are short, checking each string's characters against the set might be faster than building sets for each string. Also, Unicode normalization (e.g., NFC) is crucial for correct character comparison.
Ask about case sensitivity (case-sensitive vs. case-insensitive) and Unicode handling (e.g., normalization, grapheme clusters). Confirm if the reference string can be empty or if strings can be empty.
Use a set of characters from the reference string for O(1) membership checks. For case-insensitive, convert both to a common case (e.g., lower) before building the set and checking.
For each string in the list, check if any character is in the set. If yes, include it. This is O(n * m) where n is number of strings and m is average length, but with early exit.
Normalize strings to a standard form (e.g., NFC) before comparison to ensure characters like 'é' are treated consistently. Consider using code points or grapheme clusters depending on requirements.
If the list is large, consider preprocessing the list into sets or using bitmasks for ASCII. Discuss time/space trade-offs and potential parallelization.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.