2 DSA questions

“2 DSA questions” is not an executable problem statement. A strong interview response is to clarify the data structure or algorithm, expected output, constraints, mutability, and edge cases before choosing a solution. After those are known, explain a brute-force baseline, improve it using the relevant invariant, and state complexity. Inventing a question or answer here would mislead the learner, so this entry intentionally teaches the clarification move. In an interview, make the invariant explicit before writing code, trace a boundary example that breaks a tempting shortcut, state what each stored value represents, and explain why every update preserves correctness. This verification step also surfaces empty-input, duplicate-value, and numeric-limit cases.

Complexity: For each confirmed single-pass DSA task on n items, aim for O(n) time and O(n) auxiliary space only when a lookup structure is needed.