# jeremyevans/hs-SubsetSum

Subset sum problem solver for haskell
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```hs-SubsetSum
------------

hs-SubsetSum is a haskell library for determining the solution to the subset
sum problem [1]. The subset sum problem is NP-complete, and this is not
a very optimized version, though it is faster than a naive approach.  This
uses the meet-in-the-middle algorithm, splitting the set into two sets,
calculating all sums of the first set, and for each entry in the second
set, seeing if the difference between its sum and the final sum are in
included in one of the sums in the first set.  It returns an empty
array if it can't find a match (or the sum is 0), and an array that is
a subset of the given set that sums to the given number.

There are two separate methods provided by this library.  One is
subsetSumMap, which is a pure version that uses Data.Map.  The other is
subsetSumHash, which is an inpure version that uses Data.HashTable and
is about twice as fast.  Both versions haven been tested on ghc 7.0.4.

(1) http://en.wikipedia.org/wiki/Subset_sum_problem

Example Usage
-------------

import SubsetSum

subsetSumMap 5 [1, 2, 3]
# returns [2, 3]

subsetSumHash 4 [1, 2, 3]
# returns IO [1, 3]

subsetSumMap 7 [1, 2, 3]
# returns []

subsetSumMap 0 [1, 2, 3]
# returns []

Source
------

The most current source code can be accessed via github
(http://github.com/jeremyevans/hs-SubsetSum).

Author
------

Jeremy Evans <code@jeremyevans.net>
```