Fill the grid with zeros and ones — never three of a kind in a row, and every row and column balanced.
Find any two identical digits side by side — the cells on both ends of that pair are forced to be the other digit. Then look for gaps: a single empty cell between two identical digits must be the opposite one, or you would create a triple.
The balance rule is easy to forget. Once a row has all its zeros, every remaining cell in it is a one — regardless of what the neighbours suggest.
Each binary puzzle in Puzelo is checked by a solver written separately from the generator, using a different method. A puzzle is only published if that independent solver finds exactly one solution — so you never need to guess, and the answer we print is never wrong.