Most broken Binairo grids come from one of six mistakes, and the biggest is filling a square before it’s certain. The others are slips: only scanning rows, miscounting a long line, thinking two alike is wrong, copying another line with the last two squares, and tapping one time too many. Each one is below, with how to spot it.
If you’re new, the rules and how to solve pages explain the ideas these mistakes go wrong on.
1. Filling a square before it’s certain
When a square could go either way, it’s tempting to pick one and see. Sometimes a rule breaks straight away. Usually it doesn’t. We took every one of the game’s levels, filled one empty square with the wrong colour, and kept making honest moves until the game’s red mark appeared:
| Track | Moves before the red mark (median) | Still unnoticed after 10 moves | Longest |
|---|---|---|---|
| Easy 6×6 | 7 | 21 of 50 | 22 |
| Medium 8×8 | 21 | 36 of 50 | 39 |
| Hard 10×10 | 33 | 37 of 50 | 58 |
On two Medium levels the mark never showed at all: the moves ran out first, with the grid wrong. Here’s one on Medium level 1, with a wrong square in row 1, column 1:
Twenty-one honest moves later, rows 2 and 5 come out exactly the same, which the rules don’t allow. Neither of them contains the wrong square.
How to avoid it: only fill a square when a pair, a gap, a count or another technique makes it certain. If it could still go either way, leave it and work somewhere else.
2. Only scanning rows
The rules are the same down a column as along a row, but it’s easy to sweep the rows and forget the columns. On the game’s levels, 48% of the moves are on columns, in every track. Miss them and you’ll think you’re stuck when half the moves are still waiting.
How to avoid it: sweep the columns as carefully as the rows, and after every move, look at both the row and the column of the square you filled.
3. Miscounting a long line
On a 10×10, a line needs exactly five of each colour. It’s easy to count four as five on a long, half-filled line, and fill the rest with the wrong colour.
How to avoid it: count both colours, not just one. Five plus five must make ten, and if the empty squares don’t add up, count again.
4. Thinking two alike is wrong
Two of the same colour side by side is fine. Only three in a row breaks the rule. Two alike isn’t a problem to fix: it’s a clue. The squares at either end of them must be the other colour.
How to avoid it: when you see two alike, use them. That’s the pairs technique.
5. Copying a line with the last two squares
When a line has two squares left, one of each colour, both ways can look fine. But if another line running the same way already has the rest of it, one way would copy that line, and that’s against the rules. On the game’s levels, 41 of the 50 Medium puzzles and 38 of the 50 Hard ones have at least one spot like this.
How to avoid it: before you fill the last two squares of a line, check whether a finished line matches the rest of it. If one does, fill them the other way round from it. See no repeats.
6. Tapping one time too many
A tap cycles a square from empty to yellow to teal, and back to empty. A quick double tap meant for teal can land on yellow, and a triple tap empties the square again.
How to avoid it: look at the square after you tap it. On a computer, right-click goes the other way, straight to teal. Undo takes back a tap.
How to recover from a mistake
- A red mark means a line breaks a rule, but the mistake may be elsewhere, sometimes a long way back. Undo to the last move you were sure of.
- Press Stuck? It rings a wrong square before anything else, so you know exactly which one.
- Stuck with no red mark? Sweep every row and column again for pairs, gaps and full counts, then look at when you get stuck.