Can you paint them all?
Turn every cell black. Each move must have an even number of black side-neighbours.
The clock starts when you reveal the puzzle.ONE MOVE CHANGES THE NEXT
Make it black.
Keep it even.
Sixteen cells.
A chain of consequences.
White cells show their black side-neighbour count. Black cells show move order.AT YOUR OWN PACE
A brain snack, with room to think.
THE ANSWER OPENS ANOTHER DOOR
Now for the lovely part.
You have an answer. Explore how it works, then take the idea somewhere new.
See why it works ↓Keep your time
REPLAY YOUR OWN ANSWER
The order is the idea.
Follow your sequence one move at a time. The green border marks the next cell; the outlined cells are its side-neighbours.
BEFORE THE NEXT MOVE
THINK ONE MOVE AHEAD
Every neighbour changes parity.
Painting one cell adds 1 to the black-neighbour count of each white cell beside it. An even count becomes odd; an odd count becomes even. A move closes some possibilities and opens others.
Two separated black cells can open a bridge between them: that white cell now has two black neighbours. This is why painting the nearest available cell is not always a useful plan.
The replay checks the count before each move. A finished black board alone would not show whether you followed the rule.
The idea to take away
When actions change the rules for later actions, plan a sequence. A possible first step does not guarantee a possible finish.