Solving the “Challenger” Cross-number Puzzle
I like a good puzzle as much as anyone. The “Challenger” puzzle, aka the International crossnumber game, appears in the daily San Francisco paper.
To solve it, you have to fill the blank squares with the numbers 1 thru 9, so that the rows add up to the total at the right, the columns add up to the numbers at the bottom, and the two diagonals add up to their appropriate totals. You can repeat numbers and you don’t have to use each number, which is helpful because there are 12 blank squares.
I’m told that in the field of Operations Research, this is known as a classic transportation problem. Apparently, this puzzle is analogous to trucks moving around the country, because a change on one route has a spillover effect on others.
One day, a long time ago, I was frustrated that I couldn’t figure out the puzzle. So, I put together this little Challenger puzzle solver spreadsheet, which can be found here.
Note: This uses Excel’s “Solver” add in, which has to be turned on, by going to Tools/Add-Ins and then making sure the box that says “Solver” is checked. This probably won’t run with the Mac version of Excel.