Question: Officer A was told by an informant that the informant had suspicions that C, in the apartment next door, was selling drugs from her (C's) apartment. During the next three nights, Officer A surveilled C's apartment and saw a wide variety of people going in and out. Officer A stopped one of them, who immediately threw away what she had in her hand. The discarded object turned out to be crack cocaine. After retrieving it, Officer A entered the apartment without a warrant and found more cocaine on the living room table. Officer A seized the drugs. Was there anything invalid about what Officer A did? State your reasons.