Card Value Problem

There is not enough problem detail here to give a correct algorithm without inventing rules. In an interview, say that clearly and ask: what values can a card have, how are cards selected or arranged, what operation is permitted, and are we maximizing, minimizing, or validating something? Request one example and the input bounds, then restate the contract in your own words. If the task involves selecting a fixed number from either end, a complement/sliding-window approach may fit; if it is scoring a hand, frequency counting or dynamic programming may fit. Do not present either as the answer until confirmed. Once requirements are known, identify the invariant, test empty and duplicate values, and state Big-O in terms of cards n and any target range.

Complexity: After the card operation is confirmed, a frequency-based pass over n cards is O(n) time and O(k) space for k distinct values.