[Haskell-cafe] Re: List algorithm

[Christian Maeder]

Henning Thielemann schrieb:
> On Mon, 21 May 2007, Steffen Mazanek wrote:
> 
>> is there an efficient algorithm that takes two positive numbers n and m and
>> that computes all lists l of numbers 0<x<=n such that sum l = m?
>>
>> For instance
>> alg 5 1 = [[1]]
>> alg 5 2 = [[1,1],[2]]
>> alg 5 3 = [[1,1,1],[1,2],[2,1],[3]]
>> ...
> 
> http://darcs.haskell.org/htam/src/Combinatorics/Partitions.hs
> 
> alg  =  flip partitionsDec

*Combinatorics.Partitions> partitionsDec 5 3
[[3],[2,1],[1,1,1]]

so [1,2] is missing. And for these partitions I've also the attached module.

*Partition> parts 3
[3,2 1,1 1 1]

Christian
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