About Sum Sudoku
How to Play
Sum Sudoku is a variant of Sudoku. The goal is to fill each row, column, and 3x3 box with the numbers 1-7 and two X's.
The Sum Clues
The numbers along the edges of the board are sum clues. The X's act as separators, dividing each row and column into groups of numbers. Each clue tells you the sum of a group.
For example, if a row's clues are "10, 8, 10" from left to right, it means:
- The numbers before the first X sum to 10
- The numbers between the two X's sum to 8
- The numbers after the second X sum to 10
Each puzzle has exactly one solution.
Basic Strategy
As another example, suppose the row's clues are "1, 9, 18". Then you know the first two squares in that row are 1, X.
It is often easier to focus first on placing the X's, and then filling in the numbers.
Don't forget about the regular Sudoku strategies! It's still a Sudoku puzzle, after all.
Example Solved Board
Here's what a completed Sum Sudoku board looks like:
Other Notes
The way I create these puzzles is start with a regular solved Sudoku board. Then, I change the 8's and 9's to X's, and using that create the sum clues on the outside of the board. Then I solve that Sum Sudoku. Most of the time, the solution is not unique, so I discard it. But anything that does have a unique solution is a valid Sum Sudoku puzzle!
An open question to me is: is it possible to create a valid Sum Sudoku puzzle, where it's impossible to change the X's back into 8's and 9's and make a solved Sudoku board?