Array-Based Problem

Do not pretend this label supplies a full problem statement. Ask what must be computed, the maximum n, whether elements can be negative, whether input order matters, and whether the caller permits changing the array. Translate the answer into a concrete invariant. For example, an in-place deduplication scan maintains that the prefix before write contains exactly the unique values seen so far; a prefix-sum map maintains an index for each previously observed sum. Explain why each update preserves the invariant and why it finds every candidate. Start a dry run with an empty array, one value, all duplicates, a solution involving the first element, and extreme numeric values. If sorting is proposed, call out its O(n log n) time and mutation cost; if a map is proposed, call out expected O(n) time and O(n) memory. This makes the discussion useful even before the interviewer supplies the missing task details.