Second Most Frequent GIF Tag

Given GIF or image metadata in a flat triple format, find the tag with the second-highest frequency under tie rules. Requirements Input is a flat List<String> such as {id1, name1, tag1, id2, name2, tag2, ...}. Count tag frequencies from the third item of every triple. Return the tag with the second-highest frequency. If all tags have the same count, return "notag". If multiple tags tie for the highest frequency, there is no second-highest tag and the return value is "notag". Time complexity should be no worse than O(N). In the onsite variant, if there are multiple second-place tags, return the first such tag by input order. Notes Candidates used or considered hashmap counting plus quickselect or heap selection, but a two-pass frequency-rank scan is enough for the stated O(N) target. Hidden tests cover tie semantics; clarify whether ties at first rank, second rank, or both should suppress the answer.