Ippitsugaki: 'written in one stroke': is the Japanese name for exactly this puzzle: trace every edge of a figure without lifting the brush. It shares its idea with the Zen enso, the circle drawn in a single breath.
How to play
Tap any node to begin. Drag from node to node along the available edges. Each edge can only be crossed once. If you get stuck, tap any empty area to reset and try a different starting point.
Objective
Trace every edge of the figure in one unbroken path from start to finish.
Strategy tips
Start from an odd-degree node (one with an odd number of edges). Euler's rule says a valid path exists only when there are 0 or 2 such nodes: and you must begin at one of them.
Before drawing anything, count edges at every junction. Nodes with 3 or 5 edges are your forced start or end points.
If you get stuck mid-path, you likely crossed a "bridge" (the only connection between two parts of the graph) too early. Reset and save bridges for last.