Daily Killer Sudoku for April 21
Number 21, ModerateThis Killer Sudoku caused quite a headache for many solvers since it 'appears' to have two solutions. Quite a few people have written in since they saw their submission mark. The alternative solution is shown using the red numbers. Our solution is the normal black numbers.
It is indeed true that both sets of numbers form a Sudoku (rows, columns and boxes don't suplicate) AND all the numbers add up to the cell clues. So why is the alternative marked wrong. Well check our description of the Killer puzzle. We have this additional rule, to quote: "We conform to the Killer convention that no cage will contain a duplicate number even if it is within the rules of sudoku".
Now check the cage marked in pink. According to the alternative solution it would have two 5's in it. We disallow this as a possible solution. The reason for this convention is that not to conform to it would make the number/cage combinations almost impossible to calculate (ie most cells would have all numbers 1 to 9 as possibles) and so render many puzzles either impossible or not much fun. Its important for the game that IF a cage has a certain number of cells AND the clue is X we can safely assume there is a fixed number of combinations because no cells duplicate (even if a cage doglegs like the example).
Do write to us further if you have any issues with this rule and we'll expand if necessary.



