[英]How to write a 'generic' mergesort in Scala?
Here is what I have so far : 这是我到目前为止:
def mergesort[T <: Ordered[T]](elements : List[T]) : List[T] = {
def merge(first : List[T], second : List[T]) : List[T] = (first, second) match {
case (Nil, _) => second
case (_, Nil) => first
case (x :: xs, y :: ys) => if (x < y) x :: merge(xs, second) else y :: merge(first, ys)
}
if (elements.isEmpty) Nil
else {
val length = elements.length
val (firstHalf, secondHalf) = elements.splitAt(length/2)
merge(mergesort(firstHalf), mergesort(secondHalf))
}
}
The problem I'm having is that this fails 我遇到的问题是失败了
mergesort(List(1, 3, 6, 3, 1, 0))
error: inferred type arguments [Int] do not conform to method mergesort's type parameter bounds [T <: Ordered[T]]
mergesort(List(1, 3, 6, 3, 1, 0))
^
Is there any way to make this work for all types which are ordered? 是否有任何方法可以使所有类型的订单工作? I though Scala would have some sort of implicit conversion to a 'rich' integer type, which I assumed would have the Ordered
trait. 我虽然Scala会有某种隐式转换为'rich'整数类型,我认为它会有Ordered
特性。
What you need is a view bound def mergesort[T <% Ordered[T]]
. 你需要的是一个视图绑定def mergesort[T <% Ordered[T]]
。 See answers to this question: Generic method to return first of two values . 查看此问题的答案: 返回两个值中的第一个的通用方法 。
This will now complie but you have some bugs in your algorithm giving you a stackoverflow error in the splitAt
line. 现在这将编译但你的算法中有一些错误,在splitAt
行中给你一个stackoverflow错误。
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