Question: What album took over two years to create and contained a song written with the help of Julia Michaels?
Context: "Sober" is a song by American singer Selena Gomez from her second solo studio album, "Revival" (2015), included as the fifth track on the record.  The song was leaked two days prior the album's release, on October 7, 2015, and was originally scheduled to be released as the album's fifth single following "Kill Em with Kindness".  Gomez collaborated with songwriters Chloe Angelides, Jacob Kasher Hindlin, and Julia Michaels, along with Norwegian duo Tor Hermansen and Mikkel Eriksen, who handled production under their stage name Stargate.  Frequent collaborator Dreamlab handled the vocal production as well as background vocals.  Driven to create a unique sound for herself, the singer focused on lyrics that reflected personal experiences, along with referencing influential albums of her youth, specifically Christina Aguilera's fourth studio album "Stripped" (2002). "Revival" is a song by American singer Selena Gomez from her second solo studio album, of the same name, released in October 9, 2015 as the first track on the record.  Selena first teased a video of the song recording and production on her Instagram account then she teased the song again in a special Revival event on Palace Theater on September 16.  The song was written by Gomez, Antonina Armato, Tim James, Chauncey Hollis, Justin Tranter, Julia Michaels and Adam Schmalholz and was produced by Rock Mafia and Hit-Boy with Dubkiller handling the additional production.  Gomez said that the song is the most personal one on the album and she called as an "important song".  The song was first recorded in Rock Mafia Studios in Los Angeles and was finished when Gomez was in Mexico with her crew on Casa Aramara in April 2015. "Sorry" is a song recorded by Canadian singer Justin Bieber for his fourth studio album, "Purpose" (2015).  Written by Julia Michaels, Justin Tranter, Sonny Moore, Michael Tucker and Bieber; the song was produced by Skrillex and Blood.  It was released on October 23, 2015, as the second single from the album.  A dancehall-pop and tropical house song, "Sorry" contains in its instrumentation "brassy horn bleats", warm island rhythms and a dembow riddim beat.  Lyrically, "Sorry" is a plea for a chance to apologize to a lover, with Bieber asking forgiveness and a second chance to redeem himself. "Me & the Rhythm" is a song by American singer Selena Gomez from her second solo studio album "Revival" (2015).  It was released on October 2, 2015 to iTunes and other digital download platforms as the album's first and only promotional single.  The song was written by Gomez, Justin Tranter, and Julia Michaels, along with its producers Robin Fredriksson and Mattias Larsson, known as Mattman & Robin.  "Me & the Rhythm" was the last song recorded for "Revival", conceived after Gomez delayed the album's mixing to record more material with Michaels and Tranter.  Gomez has called the song a personal favorite from the album. Purpose is the fourth studio album by Canadian singer and songwriter Justin Bieber.  It was released on November 13, 2015 by Def Jam Recordings and School Boy Records.  It serves as the follow-up to Bieber's third studio album "Believe" (2012), and it was developed after the release of his collection "Journals" (2013), which saw him in a more R&B direction.  The album was created over a period of two years, in which Bieber struggled to find a musical direction for recording, scrapping each of these tracks many times.  The album features guest vocals from Travis Scott, Big Sean & Halsey, and production help from Skrillex & Diplo.  With the help of his personal friend and frequent collaborator Jason Boyd, Bieber started writing and recording with the idea of making an inspirational album that could encourage people through uplifting messages during a period of all his media scrutiny and his involvement in various misdemeanours; as well as his relationship with his former girlfriend Selena Gomez. "Uh Huh" is a song by American singer and songwriter Julia Michaels.  It was released on June 2, 2017, as the second single from her first EP, "Nervous System" (2017).  The song was written by Michaels and her frequent writing partner Justin Tranter, along with the song's producers, Mattias Larsson and Robin Fredriksson. "Used to Love You" is a song recorded by American singer Gwen Stefani for her third studio album, "This Is What the Truth Feels Like" (2016).  It was written by Stefani, Justin Tranter, Julia Michaels, Jonathan "J.R." Rotem and Teal Douville, and produced by Rotem.  After scrapping the album and its two singles, "Baby Don't Lie", and "Spark the Fire", in favor to start over, Interscope Records released "Used to Love You" as the album's first official single on October 20, 2015.  It was then serviced to mainstream radio on October 27, 2015. "Hands" is a charity single recorded by various artists for the 2016 Orlando nightclub shooting.  It was written by Justin Tranter, Julia Michaels, and BloodPop, and produced by the latter and Mark Ronson.  All of the song's proceeds benefit the families affected during the shooting, and will help cover medical costs and counseling efforts.  The song was conceived by Tranter, the day after the United States' deadliest mass shooting by a single gunman occurred. "Good for You" is a song by American singer Selena Gomez from her second studio album, "Revival" (2015).  It features vocals by American rapper ASAP Rocky.  The track was written by Gomez, Julia Michaels, Justin Tranter, ASAP Rocky, Nolan Lambroza, and Nick Monson, being produced by the latter two.  Originally, the track was conceived by the writers in 45 minutes, during a session booked by the latter.  Gomez then received the song through the trio's A&R and was entirely involved in its creative session, helping to develop it as a representation of her process of self-realization, her confidence as a young woman, and her feelings of vulnerability.  After it was reworked by Lambroza, she sent the song to Rocky, who added new instruments and co-produced it with his frequent collaborator Hector Delgado, who was in charge of Rocky's vocal production. "Do You Wanna Come Over?"  is a song recorded by American recording artist Britney Spears for her ninth studio album "Glory" (2016).  It was written by Mattias Larsson, Robin Fredriksson, Julia Michaels, Justin Tranter and Sandy Chila, and produced by Mattman & Robin.  The song was released as the third and final promotional single from the album on August 18, 2016, as an instant grat track for those who pre-ordered the album and for streaming.  "Do You Wanna Come Over?"  is an electropop and dance-pop song, with subtle keyboards, a strummed guitar and wobbly bass in its instrumentation.
Answer: Purpose