You can know it right away without counting the lines
Draw any shape as a graph (place points and connect them). There is a rule that lets you find out in advance whether you can draw the entire figure in one continuous stroke without lifting the pen or retracing a line.
Euler's rule: Count how many lines are connected to each point (its degree). If there are 0 vertices with odd degree, you can draw the figure in one stroke starting anywhere (the endpoint is the starting point). If there are exactly 2 vertices with odd degree, you can do it only by starting at one of those two vertices and ending at the other. If there are 3 or more odd-degree vertices, it is impossible.
Click to create a graph
💡 The person who first discovered this rule was Leonhard Euler — while solving the famous "Königsberg Bridges Problem," he helped give birth to a new field of mathematics called graph theory.