Question

我有这个代码将两个列表联合起来：

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

然而，这并没有给我我想要的结果;我希望结果与最小的结果一致。我该怎么做呢？

Answer 1

如果两个参数已经排序，那么你可以迭代它们并将更小的元素添加到结果中：

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)

Answer 2

即使您的输入未排序，这也会有效：

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

f＃顺序的两个列表的联合

2 个答案: