归并排序

//提供的int排序的统一方法
val intSort = msort((x:Int,y:Int)=>x<y) _
//逆序
val reverseIntSort = msort((x:Int,y:Int)=>x>y) _

def msort[T](less:(T,T)=>Boolean)
  (xs:List[T]):List[T]={
    def merge(xs:List[T],ys:List[T]):List[T]=
      (xs,ys) match {
        case (Nil,_)=>ys
        case (_,Nil)=>ys
        case (x::xsl,y::ysl)=>
          if(less(x,y)) x::merge(xsl,ys)
          else y::merge(xs,ysl)
      }
    val n=xs.length / 2
    if(n==0) xs
    else{
      val (ys,zs)=xs splitAt n
      merge(msort(less)(ys),msort(less)(zs))
    }
  }