list - 两个列表按顺序并集 f#

Question

我有这段代码将两个列表结合起来:

let rec union list1 list2 =
    match list2 with
    | [] -> list1
    | x::xs when mem x list1 -> union list1 xs
    | x::xs -> x::(union list1 xs)

但是，这并没有给我想要的结果；我希望结果按最小的第一个顺序排列。我该如何去做呢？

Answer 1

如果两个参数已经排序，那么您可以迭代它们并向结果添加较小的元素:

let rec union list1 list2 =
    match list1, list2 with
    | [], other | other, [] -> other
    | x::xs, y::ys when x < y -> x :: (union xs list2)
    | x::xs, y::ys -> y :: (union list1 ys)