Seeking wisdom: I have a set of number sequences, given a length parameter n, and minimum occurance parameter m, I'd like to find common continuous subsequences of length n that occur at least m times. Here's an example:

@a = ( [2,5,10,5,12,6,21,5,10,12,23],
       [5,6,11,10,5,10,6,21,5,1,9],
       [6,5,10,15,21]
    );
$m = 2;
$n = 2;
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I'd like the result to be the set containing the following sequences (hopefully I haven't missed any):

(5,10) #which occured twice in 1st, once in 2nd and 3rd
(10,5) # which occured once in 1st and 2nd
(6,21,5) # which occured once in 1st and 2nd
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performance is a concern since both the length and the number of sequences can be pretty big, say 1000. Thanks.

Update: I meant "at least length n". The subsequence does need to be in different sequences, but I'd like to have a total count including multiple occurances within the same sequence.

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