F#:整数到整数对 [英] F#: integers to pair of integers

问题描述

我有一个函数，该函数将一个整数列表作为参数，并返回一个成对的列表作为结果.例如，[1;2;3;4]应该返回为[(1, 2); (3, 4)]

I have function that takes a list of integers as an argument and returns a list of pairs as a result. For example the [1;2;3;4] should be returned as [(1, 2); (3, 4)]

我已经实现了以下功能.

I have implemented the below function for this.

let listToPairList (list: int list) = 
  let index,pairList = List.foldBack(fun elem (iAcc,listAcc) -> 
    if (iAcc % 2 = 0) then
      (iAcc - 1,(elem,list.[iAcc + 1])::listAcc)
    else
      (iAcc - 1,listAcc)) list (list.Length - 1, [])
  pairList

现在，我想使用foldBack函数但不使用索引来做到这一点.谁能给我一个关于如何制作的想法?

Now ,I want to do it with using foldBack function but without using indexes. Could anyone give me an idea about how to make it ?

任何帮助将不胜感激.

推荐答案

为什么要使用折返?

一个简单的递归函数

let rec listToPairList = function
    | []       -> []
    | x::[]    -> [(x,x)]
    | x::y::xs -> (x,y)::listToPairList xs

或者是尾递归的:

let listToPairList lst =
    let rec aux acc = function
        | []         -> acc |> List.rev
        | x::[]      -> (x,x)::acc |> List.rev
        | x1::x2::xs -> aux ((x1,x2)::acc) xs
    aux [] lst

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