Haskell嵌套列表 [英] Haskell nested lists

问题描述

我是Haskell编程的新手，我正在尝试检查嵌套列表中对角相邻的元素是否互不为负. 我的职能是:

I'm new to haskell programming and I'm trying to check if the diagonally adjacent elements in the nested lists are not negative of each other. I have my function as:

checkNegation :: [[Int]] -> Bool

示例:checkNegation[[1,2], [3, -1]]将返回False checkNegation [[1,2],[-1,3]]将返回True.

Example: checkNegation[[1,2], [3, -1]] will return False checkNegation [[1,2],[-1,3]] will return True.

推荐答案

我建议将问题分解为几个步骤.

I would suggest breaking the problem into steps.

第1步:编写一个函数以获取对角线元素:

Step 1: Write a function to get the diagonal elements:

diag :: [[a]] -> [a]

您可能会发现此问题很有帮助.

You may find this question helpful.

第2步:您想检查结果列表中的相邻元素是否彼此相反:

Step 2: You'd like to check if the adjacent elements of the resulting list are negatives of each other:

allAdjNeg :: [Int] -> Bool

其中allAdjNeg [-1,1,-1,1] = True.

这也可以很容易地逐步完成.在步骤2(a)中，检查每对相邻的元素.您也许可以将答案调整为这个问题来编写一个函数:

This, too, might be most easily done in steps. In step 2(a), check each pair of adjacent elements. You may be able to adapt the answer to this question to write a function:

adjNeg :: [Int] -> [Bool]

提示:如果定义一个函数isNeg x y = x == -y，则它是一个类似于(-)的二进制运算符，并且可以与zipWith相同的方式使用.

Hint: If you define a function isNeg x y = x == -y, this is a binary operator just like (-) and can be used with zipWith in the same way.

在步骤2(b)中，您想查看adjNeg返回的列表[Bool]是否为True. and :: [Bool] -> Bool功能在这里将很有帮助.那应该允许您定义allAdjNeg.

In step 2(b), you want to see if the list [Bool] returned by adjNeg is all-True. The and :: [Bool] -> Bool function will be helpful here. That should allow you to define allAdjNeg.

然后，您的最终功能将类似于:

Then, your final function will be something like:

checkNegation :: [[Int]] -> Bool
checkNegation lsts = not (allAdjNeg (diag lsts))

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