P,np,npc,npc-hard

P: problems that can be solved in polynomial time

NP: Can not be resolved in polynomial time or uncertain can be solved in polynomial time, but in the polynomial time to verify the problem

NPC:NP complete problem, all NP problems can be reduced (reducibility) to its NP problem in polynomial time , that is to solve the NPC problem, all NP problems are solved.

NP-HARD:NP is difficult, and all NP problems can be reduced (reducibility) to its problem (not necessarily NP-problem) in polynomial time.

Refer to: https://www.zybuluo.com/chanvee/note/12722

P,np,npc,npc-hard