Mastermind (board game)

Mastermind is a simple code-breaking board game for two players, invented in 1970 by Mordecai Meirowitz, an Israeli postmaster and telecommunications expert.

The game is played using:

a decoding board, with a shield at one end covering a row of four large holes, and twelve additional rows containing four large holes next to a set of four small holes;
code pegs of six different colors, with round heads, which will be placed in the large holes on the board; and
key pegs, some colored, some white, which are flat-headed and smaller than the code pegs; they will be placed in the small holes on the board.

The two players decide in advance how many games they will play, which must be an even number. One player becomes the codemaker, the other the codebreaker. The codemaker chooses a pattern of four code pegs. Duplicates are allowed, so the player could even choose four code pegs of the same color. The chosen pattern is placed in the four holes covered by the shield, visible to the codemaker but not to the codebreaker.

The codebreaker tries to guess the pattern, in both order and color, within twelve turns. Each guess is made by placing a row of code pegs on the decoding board. Once placed, the codemaker provides feedback by placing from zero to four key pegs in the small holes of the row with the guess. A colored key peg is placed for each code peg from the guess which is correct in both color and position; a white peg indicates the existence of a correct color peg placed in the wrong position. Once feedback is provided, another guess is made; guesses and feedback continue to alternate until either the codebreaker guesses correctly, or twelve incorrect guesses are made.

The codemaker gets one point for each guess a codebreaker makes. An extra point is earned by the codemaker if the codebreaker doesn't guess the pattern exactly in the last guess. The winner is the one who has the most points after the agreed-upon number of games are played.

In 1977, Donald Knuth demonstrated that the codebreaker can solve the pattern in five moves or less, using an algorithm that progressively reduced the number of possible patterns. Subsequent mathematicians have been finding various algorithms that reduce the average number of turns needed to solve the pattern: in 1993, Kenji Koyama and Tony W. Lai found a method that required an average of 4.340 turns to solve, with a worst case scenario of six turns.

Varying the number of colors and the number of peg positions results in a spectrum of Mastermind games of different sizes and shapes. In December 2005, Jeff Stuckman and Guo-Qiang Zhang showed in an arXiv article that the Mastermind Satisfiability Problem is NP-complete, thus explicate the computational property that makes the game intrisically interesting to play.

Since 1971, the rights to Mastermind have been held by Invicta Plastics of Oadby, near Leicester, UK. They originally manufactured it themselves, though they have since licensed its manufacture to Hasbro in most of the world, and two other manufacturers who have the United States and Israel manufacturing rights.

Computer and Internet versions of the game have also been made, sometimes with variations in the number and type of pieces involved. It can also be played with paper and pencil.

Moo and Bulls and Cows

Mastermind is similar to moo, a computer program written in the late 1960s by J. M. Grochow at MIT in the PL/I computer language for the Multics operating system. It, in turn, is similar to a game called Bulls and Cows.

Bulls and Cows is a game with numbers that may date back a century or more, and a probable inspiration for Mastermind. It is played by two opponents.

On a sheet of paper, the players each write a 4-digit secret number. The digits must be all different. Then, in turn, the players try to guess their opponent's number who gives the number of matches. The matching digits, if on their right positions, they are "bulls", if on different positions, they are "cows". Example:

Secret number: 4271
Opponent's try: 1234
Answer: 1 bull and 2 cows. (The bull is "2", the cows are "4" and "1".)

The first one to reveal the other's secret number wins the game. As the "first one to try" has a logical advantage, on every game the "first" player changes. In some places, the winner of the previous game will play "second". Sometimes, if the "first" player finds the number, the "second" has one more move to make and if he also succeeds, the result is even.

The secret numbers for Bulls and cows are usually 4-digit-numbers, but the game can be played with 3 to 6 digit numbers (in every case it is more difficult than with 4).

The game may also be played by two teams of 2-3 players. The players of every team discuss before making their move, much like in chess.

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Moo and Bulls and Cows

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