Lights Out

Lights Out, the classic 5×5 toggle puzzle. Each cell is either on or off. Tapping a cell flips its state along with the four orthogonal neighbours; tap until every cell is off. Every starting position is solvable by construction — no luck involved, only sequencing.

Tap any lit (or unlit) cell to toggle it together with the cell above, below, left, and right. The round ends when every light is off. Score is the number of clicks; lower is better. Pick a difficulty (5, 10, or 18 starting shuffles) for shorter or longer puzzles.