Lines 0
Fewest possible 0
Best –
How to play
Goal
Draw the whole shape without lifting your pen: every line exactly once, and no line twice.
How it works
- Tap any point to start. Glowing points are the ones you can draw a line to next.
- Tap a glowing point to draw the line to it. A line you have drawn turns blue and cannot be used again.
- Stuck, or took a wrong turn? Tap the point you just came from, or press Undo, to step back.
- Every shape can be done. The game counts every line you draw, even ones you take back, so try to need none.
Tips
- Count the lines meeting at each point. If a point has an odd number of lines, a route must start or end there.
- If exactly two points have an odd number, start at one of them. If none do, you can start anywhere.
- Try to leave the points with the most lines for later, so you do not get trapped.
The history of One Stroke
In 1736 the Swiss mathematician Leonhard Euler studied a puzzle from the town of Königsberg in Prussia: could a walker cross each of its seven bridges exactly once? He showed that it was impossible, and the way he reasoned about points and lines is seen as the start of graph theory, the mathematics behind maps, networks and routes today. His rule about points with an odd number of lines is the tip given on this page.