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The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] shell script challenge - Now MD5sum erratia
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Re: [vox-tech] shell script challenge - Now MD5sum erratia



Samuel Merritt writes:
 > 
 > Micah Cowan writes: 
 > > [snip]
 > > But it's a heluva lot better than running diff from one file to every
 > > other file - a factorial-time operation! :)
 > 
 > I think it's only quadratic-time. If you have N files, you need to diff
 > every possible pair of files to make sure that all the files are unique.
 > So,  you pick a file F, and compare it with all the other N-1 files. Since
 > you have to do this for all N files, and diff(file1, file2) is the same as
 > diff(file2, file1), that's only N(N-1)/2 diffs that have to be done. 
 > 
 > This is exactly like a question you see in math puzzle books sometimes: If
 > there's a group of N people and each person shakes hands with every other
 > person, how many handshakes are there? 

Sorry: I was thinking of sums and not multiplication (which is what
factorial is). I meant: N + N-1 + N-2 + ... + N-(N-1), which is
equivalent to N(N+1)/2.

-Micah
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