  Rikudo is a number-placement puzzle, where the player is asked to complete a
Hamiltonian path on a hexagonal grid, given some clues (numbers already placed
and edges of the path). We prove that the game is complete for NP, even if the
puzzle has no hole. When all odd numbers are placed it is in P, whereas it is
still NP-hard when all numbers of the form $3k+1$ are placed.
