Permanent December - Tik Tok - California Gurls are the Same Song

Well maybe not exactly the same, but somewhat similar. Someone noticed that Permanent December by Miley Cyrus, Tik Tok by Ke$ha and California Gurls by Katy Perry all have similar arrangements with the chorus and other key parts of the song matching up. I know when I first heard Permanent December it reminded me of Tik Tok. I wouldn't have thought California Gurls was that similar though.