Check that a drawing puzzle can be traced without lifting the finger

A puzzle that asks the player to trace every line exactly once only works if the picture allows it, and a made-up shape often does not. This entry gives a quick test for any shape, tells you where the player must begin, and names the trap that fools the obvious test.

Why this works

Every time you pass through a dot you use two lines, one in and one out. So only the start and the end can have an odd number of lines, and the shape must be one piece; both conditions are easy to count.

When not to use it

It only covers tracing each line once. If the player may repeat lines, lift the finger a set number of times, or draw curves that cross, the rule changes and you need another test or a longer path search.

In the full entry

• What to build, step by step
• Starting values and the reason for each
• 4 common mistakes and the fix
• A diagram of every state
• 32 lines of example code with 5 checks that pass
• How your AI shows you that it works

Say this to your AI

Use the Spielerando entry "Check that a drawing puzzle can be traced without lifting the finger" (read_entry one-stroke-drawing-possible-check) in my game. Build it step by step, and show me how you checked that it works.

Or skip this and connect the MCP: your AI then finds all of this by itself.Connect the MCP