在Haskell中旋转一个列表 [英] Rotate a list in Haskell

问题描述

我有一个定义 a 的定义，

I have a list a defined,

let a = ["#","@","#","#"]

如何旋转 @ 两个空格，以便它像这样结束？

How can I rotate the @ two spaces, so that it ends up like this?

["#","#","#","@"]

工作，

I thought this might work,

map last init a

但是语法可能不同，因为map只能用于一个函数？

but maybe the syntax has to be different, because map can only work with one function?

推荐答案

为了完整起见，一个兼容空列表和无限列表的版本。

For completeness's sake, a version that works with both empty and infinite lists.

rotate :: Int -> [a] -> [a]
rotate _ [] = []
rotate n xs = zipWith const (drop n (cycle xs)) xs

然后

Then

Prelude> rotate 2 [1..5]
[3,4,5,1,2]

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