The First Repeated Card

You flip cards one by one — the game ends the first time you flip a card you've already seen. 🎴

You get a list of cards (a repeat is guaranteed). Print the first card that appears for the second time.

Example:

Input: cards = ["sun", "moon", "star", "moon", "sun"] Output: moon

"sun", "moon", and "star" are all new the first time. The second "moon" is the first card seen a second time.