Question 74
A $3 \times 3 \times 3$ cube is made out of 27 subcubes. On every face shared by two subcubes, there is a door allowing you to move from one cube to the other. Is it possible to visit every subcube exactly once if
(a) You may start and end wherever you like
(b) You must start at the center subcube?
(a) You may start and end wherever you like
(b) You must start at the center subcube?