Phil,
JD wrote:
I would like to know if there is any interest in an implementation of the edit distance algorithm
I have an implementation of the "diff" (i.e. edit script) algorithm here:
http://svn.anyterm.org/anyterm/trunk/common/diff.hh http://svn.anyterm.org/anyterm/trunk/common/diff.cc
The "edit distance" is in there somewhere.
I would welcome this sort of thing in Boost. But it needs to be the best-known algorithm. IIRC, there was one improvement that I found in the literature but didn't implement because I didn't fully understand it.
Please correct me if I'm wrong, but I get the impression that your code is O(NM) where N and M are the sizes of the two input strings. The algorithm that I implemented is O((N+M)D) where D is the edit distance in the worst case, and typically O(N+M+D^2). The algorithm is described in the .cc file linked above. Also, your code seems to have O(NM) space requirement; I'm not sure what the lower bound is, but I think it's probably O(N+M).
I improved the algorithm and now the space requirements falls to O(m). Computational is still the same, however. Having a very quick look at your algo (in diff.cc) I can see it's more complex in a way that it is not understandable at first read. As I can see in the Boost Guideline (http://www.boost.org/more/lib_guide.htm#Guidelines): "Aim first for clarity and correctness; optimization should be only a secondary concern in most Boost libraries." So I think unless there is an obvious way to reduce computational cost to O(m) (the same way it was obvious to reduce space usage to the same), I think we should stick to the original algorithm. Thanks for your insights and further remarks, Pavol, Did you have time to take a look? If not, I've just uploaded the new version to the Vault here (http://minilien.com/?gSIPLYyR08). Thanks for your remarks, JD