Can a landlord enter your apartment or let police officers in without your concent.

No, but if the police officers have a search warrant, they can bust down the door if they want to, and the landlord would probably rather not pay for the door.

They have to give you enough notice if the're doing an inspection

If there is an emergency situation, then yes. If they have a warrant the landlord can open your apt door and let them in. If they have no warrant, then no, the landlord does not have to let them in.

Ok, landlord, yes they do not need your permission, but they have to give you notice. I may post a notice on the door 24 hours before I go in. Or call and tell them, they can't tell me NO I can't go in, all the landlord has to do is give notice.

Also if there is an emergancy, lets say landlord thinks there is a water leak, or electrical issue, they can come in without notice.

The police will need a warrant to enter or believe there is a crime in progress OR>>> there is normally an exception if the officer can prove that by waiting, the evidence would be destroyed.