Semaine 20 - Shuffling cards
- Pile shuffle
- Cards are simply dealt out into a number of piles, then the piles are stacked on top of each other. Though this is deterministic and does not randomize the cards at all, it ensures that cards that were next to each other are now separated.
- Overhand shuffle
- With the pack help in one hand, small packets of cards are released a packet at a time so that they drop on the top of the pack accumulating in the other hand.
- Riffle shuffle
- Shuffle done in two steps: Split the cards exactly in half (a bottom half and a top half) and then interweave each half of the deck such that every-other card came from the same half of the deck.
- In shuffle
- Type of perfect riffle shuffle that moves the top card to be 2nd from the top.
- Out shuffle
- Type of perfect riffle shuffle that keeps the top card on top and the bottom card on bottom.
- Gilbert-Shannon-Reeds model
- This model is a probability distribution on riffle shuffle permutations that has been reported to be a good match for experimentally observed outcomes of human shuffling, and that forms the basis for a recommendation that a deck of cards should be riffled seven times in order to thoroughly randomize it.
- Begin by flipping a fair coin n times, to determine for each position of the shuffled deck whether it comes from the first packet or the second packet. Then split into two packets whose sizes are the number of tails and the number of heads flipped, and use the same coin flip sequence to determine from which packet to pull each card of the shuffled deck.
- Double nickel
- This cheat always works because pile shuffling is not random. Start with 40 cards numbered 1 through 40. The first eighteen are land cards. Do ye olde five-pile table. Now do a second five-pile. When we chunk them back into one forty card pile "deck" what do we see? A perfect distribution of land and spells!
- Mana weaving
- Commonly, [Magic: The Gathering] players mana weaving will separate their deck into two piles, one for spells and one for land. At this point, they arrange the cards in a set pattern: two spells, one land, two spells, one land, and so on. In a 60 card deck with 20 land cards, this leaves the deck in a nice 2:1 ratio of spells to land and assures that the player will draw plenty of land.