Haskell生成列表的列表 [英] Haskell generate list of lists

问题描述

  generate :: Num n => n  - > [[n]] 
  

其中list是n元组，n是来自参数。

此外，这些清单必须进行排序。

例如：

  generate 2 = [[0,0]，[0,1]，[1,0]，[1,1]，[0,2]，[ 1,2]，[2,0]，[2,1]，[2,2]，[0,3]，....] 
  

我只能使用基本功能。

我知道它确实很简单，但我不知道如何做到这一点，我也无法在互联网上找到它。

我会很乐意提供任何帮助。

解决方案

以下是 allTuplesWithMaxElem 函数的提示...

假设您想从数字 [0..2] 中生成所有列表 [a，b，c，d] 2>必须出现作为其中一个元素的限制。

考虑以下问题：

 如果我们设置a = 0，[b，c，d]有什么可能性？ 
如果我们设定a = 1，那么[b，c，d]有什么可能性？ 
如果我们设定a = 2，[b，c，d]有什么可能性？ 
  

I am preparing for test in haskell and I found a task from last test where was given to generate infinite list lists.

generate :: Num n => n -> [[n]]

where list is n-tuple, n is from parameter.

moreover the lists has to be sorted.

For exaple:

generate 2 = [[0,0],[0,1],[1,0],[1,1],[0,2],[1,2],[2,0],[2,1],[2,2],[0,3],....]

I have to use only basic functions.

I know that it surely is simple, but I dont know how to do it and I also can't find it on the internet.

I will be really glad for any help.

解决方案

Here's a hint for the allTuplesWithMaxElem function...

Suppose you want to generate all lists [a,b,c,d] from the numbers [0..2] with the restriction that 2 must appear as one of the elements.

Consider these questions:

If we set a = 0, what are the possibilities for [b,c,d] ?
If we set a = 1, what are the possibilities for [b,c,d] ?
If we set a = 2, what are the possibilities for [b,c,d] ?

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