[ Editor: Two players each hold all the cards of one suit; on each trick both lay a card face down, the...
competition/games/gops New
New entry, edited from material collected for the archive and not yet in a released version.
Problem
[ Editor: Two players each hold all the cards of one suit; on each trick both lay a card face down, the higher card wins the trick, equal cards are put aside, and whoever takes more tricks wins. Is there a strategy? ] [ Editor: In more detail: ] the first person has all the spades and the second person has all the hearts. For each "trick", each person chooses a card from his hand and lays it face down on the table. Then they turn the cards over and the person who laid the higher card wins the "trick". If the cards were equal they are put aside. Play continues in this manner until all cards are gone. Each player's score is the number of tricks he took. The one with the higher score wins. You can also consider an idealized version in which each player starts with cards 1,2,...,n of some distinct "suit". How can you even analyze such a thing? [ Editor: The game is described in a Martin Gardner book. ]
Show solution
My recollection of this game [ Editor: omitted here: "(although I've not been able to locate the reference)" ] is that it was called GOPS (standing for Game Of Pure Strategy) [ Editor: omitted here: ", but that it had an important complication that you don't mention (and one that makes it MUCH more interesting to play)" ]. A third suit is used as the values for the tricks. In the random version, it is shuffled, and the cards in this suit are revealed one at a time. For each one, the players "bid" with the cards remaining in their own suit, and the person bidding the highest wins the card being bid for. If we let Ace count as 1, up to King counting as 13, then the total to be bid for is 91. Furthermore, in the version that I play, ties are not discarded but become part of what is being bid for on the next round. The only time not all the cards will be won by some player is when there is a tie on the last round. Two comments. First, in actual play, I have found that the following strategy works well against beginners: bid two higher than the value of the card being bid for (bid 3 for 1, 4 for 2, ... 13 for 11, 1 for 12 and 2 for 13). This will likely result in your losing the 13 and the 12, but that is only 25 points, and you'll win most of the rest. Of course, once the game gets near the end, you can exactly analyze the possibilities to maximize your score (e.g., if you have cards 7 and 8 left, and the other guy has 4 and 7, then obviously you bid 7 first, and you'll win both cards, but if you bid 8 first you might tie on the last card). One point of protocol: the cards that have been used in the bidding are discarded but left face up, so that players need not have good memories, only good analytic abilities! Second, several years ago I had a computer analyze this game, under the assumption that the cards came up in some fixed order, for n=1,2,3,4,5,6 (rather than n=13), using the techniques of 2-person zero-sum game theory (see The Compleat Strategyst by J. D. Williams (revised edition published by McGraw-Hill, 1966) for a good introduction to the subject). The results were interesting. Assume that the prize cards come up in the order 6,5,4,3,2,1. Then at your first turn you should play your 6 58% of the time, your 3 26% of the time, and your 4 16% of the time. Using this strategy, your opponent cannot expect to beat you in the long run (i.e., over many plays of the game), and if he is not also using the game-theoretic best strategy, then you will win more often than not. For example, if the opponent always plays 5 to the first trick, then the strategic player will win 62% of the time, if he continues to use the strategy that the theory calls for (of course, he needs to have the computer analyze each position as it comes up and compute the probabilities for his play at each turn). -- Jerrold W. Grossman <grossman@vela.acs.oakland.edu> The game is called "gops" (Game Of Pure Strategy) and is best played with two players although it can be played with three. The rules of the game are simple: Player A is given all of the diamonds, player B is given all of the hearts and all of the spades are placed in a pile between the two players. Each card is valued as its pip value, 2, 3, 4, etc. [ Editor: "etc" in the original ], Ace is 1 and Jack, Queen, and King count 11, 12 and 13. A spade is turned over and shown to both players. Each player bids for the spade by taking a card out of his hand and placing it face down on the table. The cards are then turned over and the highest card played (heart or diamond) gets to keep the spade; [ Editor: "," in the original ] if a tie occurs then the spade is not kept by either player. Cards are only used once. After all 13 cards have been played, the winner [ Editor: "winer" in the original ] is determined by who has the greatest total spade points. The strategy is simple: Based on previous play, determine what card your opponent is going to play and then play 1 higher. If he plays a King then play your Ace. In this manner he will get one trick (at most 13 points) you will take all the rest and beat him 114 to 13. [ Editor: the spades total 1+2+...+13 = 91 points, so the score would be at least 78 to at most 13. ] The three man game is similar, each player gets all of the hearts, diamonds, and clubs. A clear winner keeps the spade, a three way tie tosses the card out, and if a two way tie occurs, the spade is placed in a pile between the two winning players. In the final count, the value of the pile is split two ways between the winning players, with each player getting half the points. -- Bert Sheldon <berts@empros.com>