func qckSort<T: Comparable>(v: T[]) -> T[] {
    switch v {
    case []:
    return []
    default:
        let head = v[0]
        var tail = v.copy()
        tail.removeAtIndex(0)
        return qckSort(tail.filter({$0 <= head})) + [head] + qckSort(tail.filter({$0 > head}))
    }
}