Guess the artists

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Across
  1. 2. Happier Than Ever
  2. 4. Last Friday Night
  3. 6. All I want for christmas if you
  4. 7. Locked out of Heaven
  5. 9. Don't Blame Me
Down
  1. 1. Oops! I did it Again
  2. 3. Deja Vu
  3. 5. Party In the U.S.A
  4. 8. 7 rings