Deduction from clues
Code Breaker
Crack a hidden four-symbol code in eight guesses or fewer. After each guess, the counter shows how many codes could still be the answer.
How to play
- Choose four symbols and check your guess. Symbols can repeat.
- A black dot means a right symbol in the right place. A white dot means a right symbol in the wrong place. The dots are not in order.
- Watch the counter of possible codes. It starts at 1,296 and you win when you hit the code.
What it trains
Deduction and information gathering: choosing the question that tells you the most, and keeping every earlier clue in mind.
Like any brain game, it makes you better at this kind of puzzle. There is little evidence that games like this raise IQ itself, so treat it as practice and fun.
Learn the trick
Open with two pairs. A first guess like A A B B tells you about two symbols at once and usually leaves a few hundred codes out of 1,296.
Only guess codes that could be right. Before each guess, check it against every clue so far. A guess that breaks an earlier clue cannot be the answer and usually wastes a turn.
Watch the counter. It shows how much each guess taught you. The best guesses split the remaining codes into many small groups, whatever the clue turns out to be.
A perfect strategy never needs more than five guesses for this puzzle (four places, six symbols). That was shown by the computer scientist Donald Knuth in 1977.