Try One Stroke Free on iPhone
Infinite puzzles. Adaptive difficulty. No forced ads.
Shape Challenge
✓ Yes — here's how to do it
Yes — and you can start from any vertex (Euler circuit).
| Vertices | 7 |
| Edges | 7 |
| Odd-degree vertices | 0 |
| Euler path possible? | ✓ Yes |
| Euler circuit? | ✓ Yes |
| Difficulty | Medium |
A lightning bolt has 7 vertices, all of even degree. According to the odd/even vertex rule, a graph with 0 odd-degree vertices can be drawn as an Euler circuit — you can start anywhere and return to your starting point.
Learn the complete odd/even vertex rule →
If you enjoyed figuring out whether a lightning bolt can be drawn without lifting your pen, you'll love One Stroke: Line Puzzle Game. It generates infinite one-stroke puzzles — every single one is guaranteed solvable, and the difficulty adapts to your skill level.
It also adds a twist: tiles flip color (black ↔ white) as you draw, and when a full row becomes one color, it clears — like Tetris meets one-stroke drawing.
Read more: Best One-Stroke Games Ranked · How to Play · Download
Yes! A lightning bolt can be drawn without lifting your pencil. It has 0 odd-degree vertices — since all vertices are even, you can start anywhere and end back where you started. This type of challenge is exactly what one-stroke puzzle games are based on.
Yes — count the points where an odd number of lines meet ("odd vertices"). If there are 0 odd vertices, start anywhere. If there are 2, start at one of them. If there are more than 2, the puzzle is impossible. This rule works for every one-stroke challenge.
One Stroke: Line Puzzle Game by CyberGame Limited is free on iPhone with infinite procedurally generated puzzles, adaptive difficulty, no forced ads, and a unique color-flipping mechanic. It's only 14.5 MB and works completely offline.
Infinite puzzles. Adaptive difficulty. No forced ads.