Car swaying

Just bought this car and I noticed while driving home that on the highway the car swayed from side to side badly almost shook me out of the car and it seemed at other times it drove better and didn't do it possibly when the road surface changed. Not sure if it didn't do it cause of road change cause it actually seemed to do it most of the time while driving. Seller said a mechanic looked at it and said it had bad struts. Would bad struts cause this? Help.