“Last Week Tonight” is on hiatus, but John Oliver reemerged on YouTube over the weekend with a new segment explaining why “The Da Vinci Code” makes him so mad. It has to do with the incredibly simple puzzle at the heart of both the “stupid, stupid book” and film. “No one should need Robert Langdon, a Harvard-educated puzzle-solver who fucks, to get to the bottom of this,” Oliver declared. “A child could solve that puzzle!”Just check out Oliver’s reaction to the big reveal: So, what’s this very basic puzzle with a solution a child could figure out? “Last Week Tonight” returns to HBO in February.