快速排序-Swift 实现

如题，上代码：

func quick_sort(arr: inout [Int]) {
           if arr.count == 0 {
               print("Data error")
           }

       _q_sort(arr: &arr, start: 0, end: arr.count - 1)
   }

   func _q_sort(arr: inout [Int], start: Int, end: Int) {

       if start >= end {
           return
       }


       var i = start
       var j = end
       let keyValue = arr[i]

       if i < j {
           while i < j &&  keyValue <= arr[j] {
               j -= 1
           }

           if i < j {
               swap(arr: &arr, i: i, j: j)
           }

           while i < j && keyValue >= arr[i] {
               i += 1
           }

           if i < j {
               swap(arr: &arr, i: i, j: j)
           }
       }

       _q_sort(arr: &arr, start: start, end: j - 1)
       _q_sort(arr: &arr, start: i + 1, end: end)
   }

   func swap(arr: inout [Int], i: Int, j:Int) {
       let temp = arr[i]
       arr[i] = arr[j]
       arr[j] = temp
   }