Given two lists, such as

@a = qw(fred bob joe jim mary elaine);
@b = qw(frank joe jim mary bob);
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What's the best way to find the largest subset of @b in @a? Here I mean the largest ordered subset: (joe, jim, mary) would be correct, but (bob, joe, jim, mary) would not.

The best (read "easiest") solution I could come up with is to join(',', @a) and then join(',', @b[$start..$end]), and then use the index function to see if (and where) the join from @b occurs in the join from @a. There must be some perl magic to do this in a more clean, faster way.

And yes, I know that what I'm asking is of quite high computational complexity. Thanks for any suggestions!