What is No duplicates?
No duplicates changes one rule of Code Breaker: the codemaker's code may not use any colour twice. With four pegs and six colours, that leaves 360 possible codes instead of 1,296, and every code holds exactly four of the six colours.
The codebreaker's guesses are not limited: a guess may still repeat a colour, and that is often useful. A guess of two reds and two blues cannot earn more than one peg for red and one for blue, because the code holds each colour at most once, so the pattern of black and white pegs tells you where those colours are not. Feedback is counted exactly as in the standard game.
The option works with every peg and colour count of the colour game. It does not apply to Bulls and Cows, where all digits always differ, or to the word code.
Rule changes
| Rule | Standard Code Breaker | No duplicates |
|---|---|---|
| The secret code | Standard Code BreakerA colour may appear more than once. | No duplicatesEvery peg has a different colour. |
| Guesses | Standard Code BreakerA colour may appear more than once. | No duplicatesUnchanged: a guess may still repeat a colour. |
| Possible codes | Standard Code Breaker1,296 with four pegs and six colours. | No duplicates360 with four pegs and six colours. |
| With blanks | Standard Code BreakerBlanks are off. | No duplicatesIf blanks are added, an empty hole counts as one more colour, so the code may hold at most one blank. |
| Other options | Standard Code Breaker4 pegs, six colours, 10 guesses and no blanks. | No duplicatesThe other options of the colour game can be set alongside it: 3, 5 or 6 pegs, 7 or 8 colours, blanks and a guess limit of 6, 8, 10 or 12. |
History
Whether a code may repeat a colour has been a choice from the start: the rules of the board game with coloured pegs, invented by Mordecai Meirowitz in 1970, tell players to decide before the game whether duplicates and blanks are allowed.
Codes without repeats also link the peg game to Bulls and Cows, the older pencil-and-paper game it is based on, in which the digits of the secret number always differ.