Binairo

Binairo is a binary logic puzzle. Every cell holds either a 0 or a 1, and a handful of cells start filled as clues. Work out the rest by pure deduction, each finished grid has exactly one solution and needs no guessing.

• Each row and each column must contain an equal number of 0s and 1s.
• No three identical digits may sit in a row, across or down.
• No two rows may be identical, and no two columns may be identical. Conflicts glow red while you work.

• Desktop: click an empty cell to cycle blank → 0 → 1 → blank. Or use the arrow keys to move and press 0, 1, or Backspace to set and clear a cell.
• Phone & tablet: tap a cell to cycle through 0 and 1, no keyboard needed. Reset and Hint buttons are always available.

• Sizes, 6×6, 8×8 and 10×10 grids of increasing challenge.
• Daily, one shared puzzle each day.
• Practice, fresh random grids on demand.

• Spot pairs: two identical digits side by side force the opposite digit on both ends to avoid a triple.
• When a line already holds all of one digit, every remaining empty cell must be the other.
• Near the end, use the no-duplicate-lines rule to break ties between two almost-finished rows or columns.

This puzzle travels under more names than almost any other: Takuzu, Binairo, Binero, Binoxxo, Tic-Tac-Logic, Binary Puzzles, Eins und Zwei, and Tohu-Wa-Vohu — "formless and empty", after the opening of Genesis.

The names usually announce which pair of symbols a given edition uses. Binary Puzzles print ones and zeroes, Tic-Tac-Logic uses noughts and crosses, Eins und Zwei uses 1 and 2, and Tohu-Wa-Vohu uses T and V. The underlying puzzle is identical in every case; only the alphabet changes.

Three rules generate all of it: no more than two identical symbols may sit adjacent, every row and column holds equal numbers of each, and no two rows — or two columns — may be the same. The last of those is what lifts it above a parity exercise, because it forces you to compare lines that share no cells at all.

Further reading: A Short History of Two Symbols

Binairo is a binary-puzzle deduction game built on three simple balance-and-uniqueness rules, in the spirit of sudoku-style logic but with only two symbols. This is an original, free browser version with daily and practice puzzles, playable instantly with no download or sign-up.

A free, original browser game on PlayPendium. No download, no install.

1. A Short History of Two Symbols

   The puzzle is younger than the iPhone. The idea it plays with, that two marks can carry everything, if you constrain them well, is three centuries deep, and still runs inside the machine you are readi