Tridoku Puzzle Books

Tridoku is Sudoku rebuilt on a triangle. Instead of a square grid of rows, columns and boxes, the puzzle is a large triangle divided into small triangular cells, and it has four rules. First, the big triangle is split into nine triangular regions, and each must hold all the numbers 1 to 9. Second, the shaded cells along the three outer edges make three more regions that each need all nine numbers, with the corner cells shared between edges. Third, shaded cells inside the grid form a triangle whose three sides make three more regions needing all nine numbers. Fourth, no two touching cells can hold the same number, and touching at a single point counts too: a cell in the centre of the grid touches twelve others.

If square grids have started to feel routine, Tridoku gives your Sudoku skills a new playground. The logic will feel familiar: you look for the one place a number can go, or the one number a cell can hold. But the triangular shape means the regions overlap in new ways, and the touching rule adds a constraint Sudoku doesn't have, so the patterns you rely on have to be found afresh. Pencil in candidates as you would in Sudoku, and look where the regions overlap: those cells are often the first to give way.

Our Tridoku series is 600 Tridoku, with 600 triangular puzzles in every book, graded in order so the challenge keeps building. There are three books. Easy to Hard is the place to start if the shape is new to you. Medium to Very Hard suits solvers who already enjoy Sudoku variants. Hard to Extreme is for experienced solvers who want a real test. With 600 puzzles each, a single book gives you a long run of solving.

Tridoku is a good choice for anyone who loves Sudoku but wants something fresh without learning a completely new kind of puzzle. There's no arithmetic, only placement and logic. It also makes an unusual gift for a Sudoku fan who thinks they've seen it all.

If you enjoy Tridoku, you may also like our Sudoku variants, from Jigsaw Sudoku with its irregular regions to Samurai and multi-grid puzzles, and Killer Sudoku, which adds cage sums to the classic grid. Futoshiki is another pure-logic puzzle with a twist on the familiar rows and columns.