Did Denny's Franchise buy out Sambo's Restaurant or Was Denny's previous name Sambo's Restaurant?

Denny's was never owned by or named Sambo's. I know many Denny's locations were Sambos in the past; I do not know how Denny's acquired these stores. I have heard that Sambo's went under and sold them in bulk to Denny's, most likely as what is called turn-keys because the transition from one chain to the other is done in a very short period of time sometimes even overnight as if you turned the key one day and it became a Denny's.