Shapedoku

Why shapes instead of numbers

Sudoku was never really about arithmetic. You never add, subtract or compare the digits; you only check whether a symbol already appears in a row, a column or a box. That makes the numbers 1 to 9 a label and nothing more, and it is why a board of nine distinct shapes plays exactly like the classic puzzle. Many people who say they are 'bad at maths' discover they are perfectly good at Sudoku once the digits are gone.

Shapes also change how the grid reads. The eye picks out a star or a crescent in a crowded row faster than it picks out a 6 among 8s and 9s, because outline and silhouette are processed before fine detail. On a busy Extreme board that small speed-up adds up, and it is the reason each shape in Shapedoku is designed to differ by outline as well as colour.

The first technique: single candidates

Almost every board opens the same way. Pick one shape, say the circle, and look at every 3 by 3 box that does not yet contain it. For each of those boxes, cross out every cell that shares a row or column with an existing circle. If only one cell survives, the circle must go there. This is called a hidden single, and on Easy and Medium boards it can solve most of the grid by itself.

The mirror technique works on a single cell instead of a single shape. Choose an empty cell and list the shapes already present in its row, its column and its box. If eight of the nine are ruled out, the ninth is the answer. This naked single is slower to spot by eye, which is exactly what the notes feature is for.

Using notes without drowning in them

On Hard and Extreme boards the easy singles run out and you need candidate notes. The trap is to fill every cell with every possibility at once, which turns the board into noise. A better habit is to note one box or one row at a time, and only when you actually need it. Smart clean-up then removes a candidate automatically whenever you place that shape nearby, which keeps the notes honest as you go.

Once notes are in, look for pairs. If two cells in the same row can each only be the square or the heart, those two shapes are locked into those two cells, and you can remove square and heart from every other cell in that row. This naked pair is the step that unlocks most boards that feel stuck, and the same logic extends to triples when three cells share three candidates.

Pointing and box-line reductions

Sometimes a shape's possible positions inside one box all sit on the same row. The shape has to end up somewhere on that row inside that box, so it cannot appear anywhere else on that row outside the box. Crossing those cells out is called a pointing reduction, and it often creates a fresh hidden single a few boxes away.

The reverse also works. If every possible spot for a shape in a row falls inside a single box, then that box's other rows cannot hold the shape. Players who learn these two moves rarely need a hint on anything below Extreme.

Choosing a mode and keeping a streak

The Daily Challenge is the same board for everyone, so it is a fair way to measure progress week to week. No Mistakes and Perfect Run reward the notes habit above: a single wrong placement ends the run, so it pays to confirm each placement with a second reason before you commit. Speed rewards the opposite skill, fast pattern scanning, and is best played once the singles techniques feel automatic.

If you want to study a board away from the app, the website solver will walk through a puzzle step by step, and the printable generator gives you boards to solve on paper. Working a few by hand is one of the quickest ways to make the techniques stick.

Is Shapedoku the same as Sudoku?

Yes, the rules are identical. Shapes simply replace the numbers, which makes the grid easier to scan.

Can I play without downloading?

Yes, play instantly in your browser at app.shapedoku.com, or download it on Google Play.