What is Takuzu?
Takuzu is a logic puzzle on a square grid. You fill every square with one of two symbols, usually 0 and 1, until the grid follows a few simple rules. It has exactly one answer, and you find it by logic alone.
The same puzzle goes by several names. Binairo is the same puzzle under another name. It was created by Peter De Schepper and Frank Coussement in Belgium. Others simply call it a binary puzzle, because every square is one of two values. And LinkedIn's Tango is built on the same rules, with suns and moons and = and × signs between some squares. You may also know it from 0h h1, which uses two colours, or as Unruly in Simon Tatham's puzzle collection. Our post on the puzzle's many names covers how the versions differ.
Takuzu rules
The classic binary puzzle rules:
- Every square holds one of two symbols.
- No three alike side by side, across or down.
- Every row and every column has the same number of each symbol.
- In most versions, no two rows, and no two columns, are identical.
Grids always have an even size, so every line can split in half. A 6×6 grid needs three of each per line. Classic grids are often bigger: 8×8, 10×10, 12×12 or more.
How our version differs
Cats & Dogs keeps the two core rules and plays like Tango:
| Classic Takuzu | Cats & Dogs | |
|---|---|---|
| Symbols | 0 and 1, or two colours | 🐱 and 🐶 |
| Grid | Even sizes, often 8×8 to 12×12 or more | Always 6×6 |
| No three alike | Yes | Yes |
| Half of each per line | Yes | Yes: three cats, three dogs |
| No identical rows or columns | In most versions | No |
| = and × signs | No | Yes |
An = between two squares means they hold the same animal; a × means they hold different ones. The signs do much of the work extra starting squares do in classic Takuzu, so a board can open with only a few animals in place. Every board still has exactly one answer, and our solver checks that you can reach it with no guessing before it goes live.
How to solve a binary puzzle
The same moves work on Takuzu, Binairo, Tango and Cats & Dogs:
- Close off pairs. Two alike side by side means both ends are the other symbol.
- Fill sandwiches. A gap between two alike is the other symbol.
- Count the line. Once a row or column has its half of one symbol, every empty square left in it is the other.
On our boards, the signs add two more:
- Follow an =. If one square is a cat, the square across the = is a cat too.
- Flip across a ×. If one square is a dog, the square across the × is a cat.
When those moves run out, look at one line with only a few gaps left. List the ways to finish it that keep the rules. If every way puts the same symbol in a square, that square is settled.
In classic Takuzu, the unique-rows rule adds one more move. When a line has two gaps left and its other squares match a finished line, the two gaps must go the opposite way round to that line. Cats & Dogs never needs it.
Want the harder steps? Our Tango strategy guide shows every move on a board, from the first glance to the last square.
Play Takuzu online, as many as you like
Many places give you one binary puzzle a day and then stop. Here you get:
- Three new boards every day, easy, medium and hard, on the Cats & Dogs page.
- Endless mode, which deals a fresh board each time you finish one, at the level you pick.
- Every past board in the archive. Nothing expires.
- A step-by-step solution for every daily board.
- A solver for any 6×6 board, if you get stuck on one from somewhere else.
It all runs in your browser on a phone, tablet or computer. There is no app to install and no account to make.