QuickSort in Swift

QuickSort.swift

func quicksort<T: Comparable>(a: [T]) -> [T] {
  if a.count <= 1 {
    return a
  } else {
    let pivot = a[a.count/2]
    let less = a.filter { $0 < pivot }
    let equal = a.filter { $0 == pivot }
    let greater = a.filter { $0 > pivot }
    return quicksort(less) + equal + quicksort(greater)
  }
}