What does algorithm correctness mean?

• A. The algorithm is the fastest.
• B. The algorithm produces the correct result for all valid inputs.
• C. The algorithm uses the least memory.
• D. The algorithm uses recursion.

Answer: (B)

Correctness in algorithms means that for every valid input, the algorithm returns the result it’s supposed to produce. In other words, the output matches the specification of the problem for all cases within the intended domain. This is about the accuracy of the result, not how fast the algorithm runs or how much memory it uses. Often we talk about total correctness: the algorithm terminates on all valid inputs and the output is correct; sometimes we also discuss partial correctness, where if the algorithm terminates, the result is correct, but termination isn’t guaranteed. You justify correctness by formal proofs or rigorous reasoning (like invariants and postconditions) or by thorough testing against the specification. The other choices mix in performance or implementation details—fastest, least memory, or using a particular technique like recursion—which don’t determine whether the algorithm’s output is correct.