So you mean subsequences of
at least length n? Do the m occurences have to be in different elements of @a? If so, do the elements have to be adjacent? (I'm trying to figure out what you mean by 'continuous'.)
Update: If you really meant at least, would you want (1,2,3,1,2,4,1,2,4) to show (1,2,4) and (1,2) or just (1,2,4)?
Update: assuming "continuous" only meant not considering (1,3,5) to be a subsequence of (1,2,3,4,5), and that you
were just abbreviating the fact that there were matching
(6,21) and (21,5) by saying (6,21,5), and assuming all
your data are integers > 0:
use warnings;
use strict;
no warnings "utf8";
my @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]
);
my $m = 2;
my $n = 2;
my $big = join "\0", map join('', map chr, @$_), @a;
$big =~ tr/\0\n/\n\0/;
my %uniq;
my @m2 = map [map ord||10, split //],
grep !$uniq{$_}++,
$big =~ /(?=(.{$n})(?s:.*?\1){${\($m-1)}})./g;
use Data::Dumper;
print Data::Dumper->new([$_])->Terse(1)->Indent(0)->Dump(), "\n"
for @m2;
but it doesn't scale well (but may scale as well as any other solution.)