A Secret Santa gift exchange is an easy way to get friends and coworkers in the giving spirit while keeping holiday spending in check. Here's the most mathematically perfect method for running your own.
In this video from Numberphile YouTube channel, Dr Hannah Fry explains why a traditional Secret Santa doesn't provide perfect anonymity. In fact, if you do it the old fashioned way with pieces of paper in a hat, you'll often end up having to start over because people will often draw their own names. If you want to guarantee anonymity, and make sure you only have to draw names once, here's what Fry suggests you do:
- Create a set of cards with two halves — a top and a bottom — for each person participating. If you have 10 people, you make 10 cards.
- One half will say, "You are number [#]," and the other will say, "You are buying for number [#]." The number should be the same for both halves. If it says, "You are number 1," on top, the bottom should say, "You are buying for number 1."
- After you've made the cards, you lay them face down and shuffle them around so you don't know what order they're in.
- Now lay them out side-by-side in a line, still face down, then cut the cards in half. Don't reveal anything yet.
- Once you've cut all the cards, shift all the top halves over by one, then combine them to make a set of new, whole cards.
- Each person then picks one of the new, whole cards.
- Lastly, you make a numbered list and everyone writes their name next to their newly assigned number.
With this method, you guarantee the number on top won't match the number on the bottom, so nobody can get their own number. And because you shuffled before you cut the cards, nobody knows which numbers are where, guaranteeing anonymity. All that's left is to set a price limit and your Secret Santa gift exchange is ready to go.
The Problems with Secret Santa [YouTube]