Spot the Doubles

Two kids brought the same trading card — after sorting the pile, identical cards stand RIGHT NEXT to each other. 🃏

You get a list of cards (numbers). Print every value that appears more than once, each printed once, smallest first, separated by spaces — or no doubles.

Example:

Input: cards = [7, 3, 7, 1, 3] Output: 3 7

Sorted, the list becomes [1, 3, 3, 7, 7] — the duplicate 3s and 7s sit right next to each other, reported smallest first.