## Archive for July 9th, 2008

### Crossnumbers

July 9, 2008

The San Francisco Chronicle carries Sudoku by the comics, but it turns out that it has an additional Sudoku-like puzzle hidden in the classifieds. And by Sudoku-like, I mean not really at all like Sudoku except that it involves digits being put into boxes. Actually, it’s more like Kakuro now that I think about it, except you can have the same digit appear more than once in a row or column. So, in fact, it’s not really like either one.

The idea is that there is a 4×4 grid with one digit in each box. The sum of each row is given on the right (shown below in bold), the sum of each column is given below the column (shown here in bold), and the sum of the diagonals is also given. In addition, some of the entries are already given.

Cross Numbers
18
3 1 12
6 19
4 18
1 4 13
23 7 17 15 11

In theory, these could be solved logically, but it turns out that (at least for the puzzles in the Chronicle) there are multiple solutions, and the practice of making a guess, checking how far off you are, and then adjusting the guess works pretty well for these.

Aside: My brother-in-law Scott, who brought these to our attention (thanks Scott!) said he’d looked around on the internet for info on this puzzle but couldn’t really find anything. This may be due to the fact that “Cross Numbers” seems to refer to more than one game: I also found a game that was more like Crossword puzzles, with teach Across or Down clue leading to a number, one digit per square. You can see an example here.