Killer Sudoku

Killer Sudoku is a striking example of a real intellectual puzzle, in which an arbitrary selection of options is not as important as an accurate mathematical calculation.

At the beginning of the game, the player has at his disposal a square playing field, divided into 9 zones. Each zone, in turn, is divided into 9 cells. Dotted lines highlight areas that can simultaneously affect 1-3 zones, and at the top of the dotted figures are numbers equal to the sum of all numbers included in the area.

Some cells on the field are already filled with numbers (usually at easy difficulty levels), you just have to fill in the rest, following simple mathematical calculations.

Game rules

The Killer Sudoku puzzle largely repeats the rules of regular Sudoku, and another popular Japanese game - Kakuro. The player's task is to fill the empty cells with numbers from 1 to 9 so that in each row, in each column and in each allocated 3x3 zone, each number appears only once. In this case, two additional rules must be observed:

• The sum of the numbers inside the dotted area must correspond to the number with which it is numbered (usually this number is indicated in the upper left part of the dotted area).
• Numbers may be repeated within a dotted line if the areas it highlights span multiple 3x3 zones. At the same time, repetitions of numbers are not allowed within each 3x3 zone.

If in most similar puzzles the dimensions of the playing field are arbitrary, then in Killer Sudoku it always has a 9x9 format. This restriction comes from the game rules themselves, according to which only numbers from 1 to 9 can be used on the field.

Game tips

Killer Sudoku is a game in which difficulty depends not on the size of the playing field, but on how full it is at the beginning of the game. In simple versions, a lot of numbers are initially open on the field, while in complex versions there are very few (or none at all). One way or another, it is worth starting the game with the so-called extreme sums - dotted areas with the largest or smallest sums of numbers.

For example, if there are only five cells in the area with the number 34, only large numbers are possible for it - from 4 to 9. If you place a three, two or one in at least one of the cells, they cannot add up to 34, but This means that these options are no longer available. But the variability still remains high: in a five-cell area with the number 25, as many as 12 options for filling the cells are possible!

Another important point is that the sum of all numbers in each 3x3 zone is always equal to the number 45. You can always build on this by calculating the sums for individual dotted areas. If some of the cells of the dotted area are located inside this 3x3 zone, they are conditionally classified as internal, and those extending beyond its boundaries are classified as external. Accordingly, you can count the numbers in them separately!