Belt Packing: Return a Triplet When 3 Items Fit a Threshold

Problem: Conveyor Belt Packing (Threshold Condition, Online Triplet Output) A conveyor belt produces items continuously. Each item has an integer size. Whenever there exist 3 items a, b, c satisfying: max(a,b,c) - min(a,b,c) < threshold those three items can be packed together. Implement a class Packer: Initialized with threshold. Method add(x) inserts a new item of size x. If after insertion there exists any valid triplet, add must immediately return one such triplet (sorted ascending) and remove those three items from the system. Otherwise return empty. Constraints 1 <= threshold <= 1e9 0 <= x <= 1e9 Up to N = 2e5 calls to add. Example threshold = 3, calling add(5), add(6), add(7) returns [5,6,7] on the third call since 7-5=2 < 3. You may return any valid triplet if multiple exist. Example Input threshold=3, add sequence: 5,6,7 Output [5,6,7] (on 3rd add)