What is Killer Sudoku?

At this point, almost everyone in the world knows what Sudoku is. Many of us sit down each day with our Sudoku book or pull up one of our many apps to see if we can knock out a puzzle or two (or maybe a dozen). There have been quite a few attempts at matching the popularity of Sudoku or trying to find a variant that catches on. Not many have been successful, though, save for one.

That’s where Killer Sudoku comes in. This game sounds terrifying on the surface level. After all, “killer” is right in the name. You may be surprised, though, as a lot of Killer Sudoku puzzles are actually easier than the standard Sudoku puzzles on the easy difficulty. Let’s take a look at Killer Sudoku, including where it came from and how to play.

History

Sudoku had been around for ages by the time the 1990s came around. There were even variants by that point, including Killer Sudoku. It wasn’t until the mid-2000s that Killer Sudoku was introduced outside of Japan, though, just as the original version of the game was starting to gain traction in the west. 

The name implies, well, almost nothing. Killer Sudoku was originally called samunamupure in Japan, which translated simply into “sum number place.” It does a much better job of explaining what the game is about compared to Killer Sudoku. The game itself was the creation of Tetsuya Nishio, a Sudoku master who wanted to offer up a new challenge.

“This new variation will be a dreadful challenge to you,” Nishio said. “Do not get too addicted. We can make these puzzles so difficult that it would take a champion six hours to complete one.” 

Structure

If you’re looking at Killer Sudoku in black and white, it may not seem so bad. The familiar 9×9 grid is there and separated into smaller 3×3 sections. What sets Killer Sudoku apart, though? Well, new boxes are added to the mix in the form of different colors. Not only that but there’s a small number in the corner of some of the boxes. The sum of the numbers within these colored “cages” must add up to that number.

There’s another variation of Killer Sudoku called ‘Killer X’ that takes things one step further by making it so that one of the diagonal lines contains one number each, as well. When first introduced, Killer Sudoku was extremely confusing for a lot of people, and the rules had to be explained by The Times in England after many spent weeks doing the puzzles wrong.

How to Win

It takes a lot of mathematical know-how and a ton of patience to figure out how to beat a Killer Sudoku puzzle. Experts say that you should start off with the cages to get the right sum and pick the cages that have the highest and lowest numbers. Once you solve those, figuring out the rest of the 3×3 box should be much easier.

There’s also another strategy that should be familiar to Sudoku players called the “Rule of 45.” The numbers in all of the houses on a Killer Sudoku puzzle should add up to 45. This can be much trickier with the cages that need to have a sum of their own. Experts will argue over which method is best for trying to solve the puzzle, but it’s up to the comfort of the player.

Summary

Just like the regular version of the game, Killer Sudoku has a lot of difficulty levels. The easiest level is the best starting spot for any player, even for those that haven’t played regular Sudoku. It’s a great introduction to the game, and when the cages are removed, players will find the standard version easier to figure out. As for the harder levels of Killer Sudoku, well, as Nishio says, it’s a “dreadful challenge.”