Yohaku

Yohaku is a math logic puzzle in the same vein as kakuro, another variation of sudoku that actually uses math. It was developed by a math teacher from Canada to help his students. The puzzle allows addition and multiplication to fill in a grid with the results for each row and column already displayed. You can use numbers or algebraic expressions in the grid. There can also be constraints added to the puzzle to make it harder or easier to solve. It turns out you can create these puzzles by essentially reverse engineering them – filling in the squares of the grid and calculating each result, and then publishing the puzzle with the results and blanking out the inputs. You can add constraints for the user to use that match the numbers you input in the generator. In this version of the puzzle on this site, the app generates a puzzle randomly from a palette of sizes, types and constraints, using the above reverse engineering technique. The user then attempts to solve it, with the app completing rows and columns when only one box is empty, and telling you when you've solved the puzzle. Integers and fractions are now used, but plans are to add algebraic expressions and other kinds of numbers later.

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