q1 sample answer

function oneHitWonder(songList) {
  const oneHits = [];

  const counter = songList.reduce((artistSongCounter, song) => {
    if (artistSongCounter[song.artist]) {
      artistSongCounter[song.artist].count++;
    } else {
      artistSongCounter[song.artist] = { count: 1 };
    }
    return artistSongCounter;
  }, {});

  for (let artist in counter) {
    if (counter[artist].count < 2) {
      oneHits.push(artist);
    }
  }
  return oneHits;
}