Kansuko
A Kansuko puzzle takes its shape and rules from a traditional Sudoku, but with slight modifications. A Kansuko puzzle consists of a three 3x3 boxes stacked on top of each other and a "Sum Column" to the right. Each 3x3 grid contains the numbers from 1 through 9. Similarly, each column contains the numbers 1 through 9, including the Sum Column.
Sum Column
The main difference from a standard Sudoku (besides its layout) is the added constraint of the Sum Column. To determine the number in the Sum Column, one adds the three digits immediately to its left, and uses only the digit in the "Singles" column. Example: 6 + 7 + 2 = 15, so a 5 would be placed in the Sum Column. The Sum Column, like the other columns, contains the digits 1 through 9. Givens for the puzzle can be located in any of the 3x9 grid cells or in the Sum Column.
Examples
Unsolved puzzle
Completed puzzle
Solving Techniques
Besides the techniques that you can use for standard Sudoku, solving a Kansuko requires a whole new set of solving techniques. It is often useful to know the combinations that add up to the desired number in the Sum Column. Simple addition can be used to help eliminate possibilities that will never add up to the number in the Sum Column. For example, given a row with a 5, 3, and a blank space - it can be immediately determined that a 2 cannot be placed in the blank space, for a zero will never appear in the Sum Column.
