Array+shuffled.swift

extension Array {
  mutating func shuffle() {
    if self.count < 2 { return }
    for i in 0..<self.count {
      let j = Int(arc4random_uniform(UInt32(self.count - i))) + i
      if i != j {
        swap(&self[i], &self[j])
      }
    }
  }

  func shuffled() -> [Element] {
    if self.count < 2 { return self }
    var copy = self
    copy.shuffle()
    return copy
  }
}