The Math Behind “Spot It” | Hacker News Reader

The Math Behind “Spot It”

smithsonianmag.com

68 pointsbobbiechen21 comments

Stand-up Maths did a video on this a few months ago. https://www.youtube.com/watch?v=VTDKqW_GLkw including creating a much larger version.

I dig this channel, but I found this particular explanation hard to follow. That's why I'm about to give the SciAm article a read.

> Kirkman had actually solved the problem three years prior, when he determined how many schoolgirls he’d need to make the puzzle work. This proof was in response to a question posed in the same magazine in 1844: “Determine the number of combinations that can be made of n symbols, p symbols in each; with this limitation, that no combination of q symbols which may appear in any one of them shall be repeated in any other.” Kirkman extrapolated this as a question of unrepeated pairs in triplets, asking from a certain number of elements, how many unique triplets can you have before you start repeating pairs?

This is not an extrapolation. It is a specialization of the problem in which p is 3 and q is 2. If either is an extrapolation of the other, it's the first one being an "extrapolation" of the chronologically-later second.

https://blog.plover.com/math/finite-projective-planes.html

No longer maintaind, but I did make django-project that automatically generated a pack from a set of images. As the kids and I loved playing a snap like game.

It rotated, random-sized etc all the images.

https://barwap.com/projects/splendid-snap/ https://github.com/bmsleight/SplendidSnap

The python script works standalone form the command-line https://github.com/bmsleight/SplendidSnap/blob/master/libspe...

There is a great explanation of the math - which is MUCH simpler to follow - at stackoverflow [1]

(I have converted that into a JS method for all the golfers here [2])

But there is more to it than just figuring out what pictures go on the card.

What's the math to make each image have a unique size? [In Dobble, there are eight images on a card and no two images are the same size. Each image is presented seven times, and the size differs each time.]

How do you ensure unique image rotation (which varies similarly to the size)? How to do collision detection so that all the images don't overlap?

Also, there are the variations. For example, what is the math to have all images matching EXCEPT one (I have seen this game for sale)?

It's fun stuff, but there is more work to do than just what the article reflect.

BTW, I would love it if someone has algorithms for the questions I raised. I have been meaning to make a SpotIt! with images of the youth in the group I work at - it would be a unifying present to give out on a overnight.

[1]: https://stackoverflow.com/a/47130477/87520

[2]: https://stackoverflow.com/a/67409457/87520

> Spot It!, in its distinctive round tin, is hugely popular—it’s in the top ten of Amazon’s list of best-selling card games, right up there with classics such as Uno and Taboo.

Taboo is not a card game.

Is it also not a classic?

It definitely is a classic, but it's not a classic card game. Is Mario Kart 8 on the list of best-selling card games too?

Mario Kart 8 comes with a deck of cards?

Depends on your definition.

Wikipedia says:

> Some games that are placed in the card game genre involve a board. The distinction is that the gameplay of a card game chiefly depends on the use of the cards by players (the board is simply a guide for scorekeeping or for card placement), while board games (the principal non-card game genre to use cards) generally focus on the players' positions on the board, and use the cards for some secondary purpose.

https://en.wikipedia.org/wiki/Card_game

Afaict, the cards in Taboo are the primary driver of the game. And so it seems reasonable to say that it is indeed a card game.

The cards are not actually used in the game. They serve only to display information. Taboo is a card game in the same sense that Trivial Pursuit is a card game, or that Werewords is a card game. And Werewords doesn't even pretend to have cards involved.

If your kids like Spot It when they were younger they (and you) may enjoy Set (https://boardgamegeek.com/boardgame/1198/set) when they get a little older.

Another great thing about Spot It is that wide age ranges can play together. There’s some correlation about older kids and adults being better, but really young kids can still easily win a few rounds and build their confidence.

I'm not sure I'd agree adults are better, my daughter has been at least as good as my wife and I since she was 6 or so, at least for most of the games. However the one where we can consistently win by a large margin is the one where 9 cards are put out and you have to find groups of 3 across them - for some reason that is much harder for her.

Highly recommend the game. While playing it is a fascinating reminder of the limits of our perception and how we pattern match.

Is this something like rapture. Invented in europe but known only in US?

In Europe it's called Dobble.

https://www.dobblegame.com/en/games/

make your own https://macrusher.github.io/dobble-generator/

There is a Harry Potter flavour one. 55 cards. Very fun.

That website is toxic on mobile without an ad blocker.

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