Each row represents a guess at a secret code. A black dot represents a digit in the guess that is in the same position as a digit in the secret code. A white dot represents a digit in the guess that is in the secret code, but not in the same position. The dots are given in no specific order, and each letter in the secret code contributes at most one dot with black dots given priority over white dots in case of ambiguity (for example, if the guess was 12334 and the codeword was 53363, the puzzle would display 1 black and 1 white).
(Rules from Puzzle GP IB, example from janko.at)
- A code can be a string of numbers, alphabets, or both.
- Sometimes rule forbids numbers and letters occurring more than once in a code.
History of the puzzle
This puzzle can be traced back to an old 2-player code-breaking game called Bulls and Cows, which is of an unknown origin.
The name Mastermind is derived from the game of the same name, invented by Mordecai Meirowitz (Israel) in 1971.