Scala 快速排序算法实现

问题描述

我需要帮助填写一些空白，以便分区在调用 partition(data,lower,upper) 时工作​​。虽然，我认为 if 语句应该是 if (lower

 object Quicksort {
  def partition[A](data: Array[A],lower: Int,upper: Int)
                  (implicit comp: Ordering[A]): Int = {
    val pivot = data(upper-1)
    var mid = lower-1
    for (i <- lower until upper-1) {
      if (comp.lteq(data(i),pivot)) {
        mid += 1
        swap(data,mid,i)
      }
    }
    swap(data,mid+1,upper-1)
    mid+1
  }
  def sort[A](data: Array[A])(...): Unit = {
    def sortRange(data: Array[A],upper: Int):
    Unit = {
      if(lower < upper) {
        val pivotIndex = partition(data,upper)
        sortRange(data,pivotIndex)
        sortRange(data,pivotIndex+1,upper)
      }
    }
    sortRange(data,data.length)
  }
  def main(args: Array[String]) : Unit = {
    //Result of partition(data,upper):
    //sortRange results in quick-sorting the range: [lower,upper)
  }
}

解决方法

由于 Quicksort 是一种就地排序算法（即它是关于副作用的），而不是传递要排序的集合，我想将方法​​“附加”到所述集合。

我还想删除所有那些讨厌的可变变量。

implicit class QSort[A:Ordering](as: Array[A]) {
  import Ordering.Implicits._
  private def swap(x: Int,y: Int): Unit = {
    val hold = as(x)
    as(x) = as(y)
    as(y) = hold
  }

  private def partition(lo: Int,hi: Int): Int =
    ((lo until hi).filter(as(_) < as(hi)) :+ hi)
      .zipWithIndex.foldLeft(0){
        case (_,(j,x)) => swap(j,lo+x); lo+x
      }

  private def quicksort(lo:Int,hi:Int): Unit =
    if (lo < hi) { 
      val p = partition(lo,hi)
      quicksort(lo,p-1)
      quicksort(p+1,hi)
    }

  def qsort(): Unit = quicksort(0,as.length - 1)
}

测试：

val cs = Array('g','a','t','b','z','h')
cs.qsort()  //: Unit
cs          //: Array[Char] = Array(a,b,g,h,t,z)

val ns = Array(9,8,7,6,5,4,3,2,1)
ns.qsort()  //: Unit
ns          //: Array[Int] = Array(1,9)