var arr = [1, 1, 8, 9, 9, 10, 10]
if (arr.count < 3){
    return 0// TODO: add proper exception because array does not match input requirements
}

if arr[0] != arr[1]{
    return arr[0]
}else if (arr[arr.count-1] != arr[arr.count-2]){
    return arr[arr.count-1]
}else{
  for i in 1...arr.count-2{
      if arr[i] != arr[i+1] && arr[i] != arr[i-1]{
          return arr[i]
          break
      }
  }
}