Party Time

function solve(arr) {
  let vips = [];
  let regular = [];

  for (const guest of arr.splice(0, arr.indexOf('PARTY'))) {
    (!isNaN(guest[0])) ? vips.push(guest): regular.push(guest);
  }

  for (let incomingGuest of arr.splice(1,)) {
    if (!isNaN(incomingGuest[0]) && vips.includes(incomingGuest)) {
      vips.splice(vips.indexOf(incomingGuest), 1);
    } else if (regular.includes(incomingGuest)) {
      regular.splice(regular.indexOf(incomingGuest), 1);
    }
  }

  console.log(vips.length + regular.length);
  if (vips.length > 0) { console.log(vips.join('\n')); }
  if (regular.length > 0) { console.log(regular.join('\n')); }
}