[Haskell-cafe] diff implementation in haskell

Bayley, Alistair Alistair.Bayley at invesco.com
Tue Dec 8 09:20:00 EST 2009

> From: haskell-cafe-bounces at haskell.org 
> [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Ketil Malde
> Don Stewart <dons at galois.com> writes:
> >     http://hackage.haskell.org/package/Diff
> Wherein we can read:
> | This is an implementation of the O(ND) diff algorithm 
> [...]. It is O(mn)
> | in space. 
> At first I thought 'N' and 'M' would be the lengths of the lists, and
> 'D' is the number of differences, but then the space bound 
> doesn't make
> sense.  I tried to find the reference, but Citeseer is down
> (again. sigh).
> Anybody know what the bounds really are?

I think the space bounds are O(M+N). Section "4b. A Linear Space
Refinement" concludes with "Unfortunately, the input sequences A and B
must be kept in memory, implying that a total of O(M+N) space is

BTW, there is a minor improvement to this algorithm (claims to be
faster, same space usage):

found via:

I thought this paper was easier to understand.

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